This is one of those topics that I researched a lot when I bought a new home recently. While LED lights seem awesome at the first sight (low power consumption! No warmup time!) when you dig a little deeper you'll find that most LEDs are far from perfect:
1. Lots of LEDs flicker. Shitty ones with twice the frequency of the main current (so 100/120 Hz) While you might not notice this it causes eye strain and can lead to eye fatigue, headaches, migraines.
2. Most LEDs have a low CRI (Color Rendering Index, or called Ra which is one standard to measure it), this means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% of a spectrum that covers most of the visible light.
If you look around you'll be able to find reasonably priced LEDs with 90+ Ra and no flicker, but its a pain in the ass to research it. Especially if you need something more special like a LED light strip for your kitchen.
No, the diodes don't, the drivers do. You are speaking to a technical audience ;)
> means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% ...
Hardly. It means that they reproduce a set of 8 or 16 fixed frequencies from the ral pallete. It doesn't cover anything inbetween so it's just a rough rule of thumb. It doesn't cover colors in the far red (or was that violette on the other end of the soecteum?) at all.
Overall, overexposure of some frequencies, arguably to appear brighter and fuller, has damaged musuem pieces--Radiation stress, really. All they can do now is individual tests with photometric instruments, because they can't trust CRI. Same for horticultural lighting, which hasn't really taken of anyway.
Edit: Some manufacturers publish reference curves in the datasheets for their emitters, however I don't know how accurate these are under varying conditions and across batches.
Having made a cheap DIY spectrometer[1], I found the spectrum of LED around my house quite good, not completely smooth as sunlight, but smooth enough (you can gain some efficiency for not being totally smooth by better matching eye receptors). It's a far cry from fluorescent spectra that have extremely sharp concentrated spectra (and I suspect the risk from narrow spectra of causing biological damage is greater, since it could in theory disrupt very efficiently some molecular energy transition that happens to be well matched with that frequency).
I'm not an expert, so take it with a grain of salt.
Electrons in molecules have discrete energy states they can occupy, per quantum mechanics (the discrete set of wafunction solutions)[1]. Consequently they can only transition between states by absorbing or emitting photons of specific energy values (I believe it doesn't have to be exact due to scattering and various QED dynamics, but it has to be very precise). If your molecule is exposed to broadband light, a few photons will match those ionization energies, however the quantity should be small[2]. If your light source contains peaks though, and there happens to be important molecules whose energy transition matches your source (a big if), you're going to get a lot of ionization.
I should have mentioned a more established issue is fluorescent lamps emit more blue/violet and UV than LEDs (LEDs are usually packaged in plastic anyways, so even if the emitted there'd be no risk of uv exposure). In common molecules the more prevalent ionization energies are UV and beyond, that's why the risk is greater.[3]
> No, the diodes don't, the drivers do. You are speaking to a technical audience ;)
I've seen 'drivers' that are nothing more than a resistor in series with the LED. So the LED, acting as a half-wave rectifier, causes the flicker. To your point, in this case the LED should be considered part of the driver.
Thanks for the corrections, yep I was a bit sloppy. But I hope the main point came trough - which is that you should choose carefully when buying LED bulbs, lots of crappy ones on the market.
> 1. Lots of LEDs flicker. Shitty ones with twice the frequency of the main current (so 100/120 Hz) While you might not notice this it causes eye strain and can lead to eye fatigue, headaches, migraines.
That's with a full rectifier. It's even cheaper to go half-rectifier and end up with 50/60Hz flicker. Being cheaper, this happens a lot.
I'm super sensitive to this flickering and will get nausea after sitting in some cheap LED lighting while other people hardly seem to notice.
I jokingly say that with cheap 50Hz LED lighting and 60fps screens, virtual reality now has a higher frame rate than real reality.
This use of half-rectified lighting is especially true of LED Christmas lights. I haven't yet dug in on how to change them to at least full-rectified, which look much better to my eyes.
Is it just a matter of adding a bridge rectifier? I guess I'd need to add some resistors in there also to dim the emitters since they'll be on twice as often (to prevent premature burn-out).
Has anybody looked into this? I'll admit to being a bit eccentric.
How does this effect compare to old fluorescent tubes? Where I live we still got a lot of those around (specially in government offices, which is as cheap as you could imagine, and then some), so LEDs seem like a win, even when horrendous.
Fluorescent tubes flicker at 100/120 Hz, but the flicker is less pronounced because the phosphor keeps giving off light for some time after the electrical current stops flowing.
White tubes are made of a mixture of phosphors, and each of them has a different time constant, meaning the flickering is noticeable as repeated changing of colors. Take a photograph (with a rolling shutter phone for example) of a fast moving object under fluorescent light and you'll see blue and yellow shadows from the changing light[1].
LEDs also use phosphors -- in that way an LED is like a miniature fluorescent tube. Just like fluorescents, LEDs (at least those used for illumination) have an undesirable emission spectrum that's converted to "white" with a phosphor coated enclosure. (LEDs generally have a very narrow spectrum, and the GaN system used for lighting can produce blue and shorter wavelengths, depending on doping.)
They are 100Hz, as I found out while trying to do an optics experiment, but they never bothered me directly. I think it has to do with LEDs going completely dark, where fluorescent just has slight fluctuations. Or maybe it is a 50Hz vs 100Hz flicker thing.
> If you look around you'll be able to find reasonably priced LEDs with 90+ Ra and no flicker, but its a pain in the ass to research it
For people in North America, I'd recommend https://www.hyperikon.com/ for LED products from screw-in bulbs to large area lights with high CRI and no flicker (note: a few products don't have high CRI, so do check the product page). They offer a good range of color temperatures too.
> Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% of a spectrum that covers most of the visible light.
That's not what Ra means. It's not a percentage - in fact, something with a perfectly flat distribution covering all the visible spectrum would not have especially high CRI, because that's significantly different from the spectrum of blackbody radiation, on which CRI is based. The actual algorithm for calculating CRI doesn't fit nicely in a comment, but it's in the Wikipedia page: https://en.wikipedia.org/wiki/Color_rendering_index
Edit: missed the negation - CRI is not high for a perfectly flat spectrum.
I just replaced all the lighting in my House a few months back with Hyperikon LED lighting, and really felt like it was an improvement over the previous CFL lighting.
This comment alleviated some of creeping anxiety from the above posts that I maybe hadn't done enough research (I hadn't, I just got lucky).
Note that CRI (Colour Rendering Index) is a bit bogus. It came about when florescent lights became a thing and was originally based on a sheet of printed colour swatches. RGB LED lighting promoters have pointed out that CRI doesn't really reflect the goodness of light sources other than florescent in practice.
I'd say CRI is a bit bogus in that a light source can have fairly high CRI and still look bad. For example, I've seen LEDs used in a flashlight with a CRI over 90 that had a significant green tint.
On the other hand, I have not seen a light source with low CRI that looked good illuminating people, natural materials, or anything else where subtle differences in color are relevant.
There are several other ways color rendering can be measured, but the ones used in the lighting industry tend to be based on comparing the rendering of specific samples much like CRI. One that's seeing a lot of use lately is IES TM-30, which is based on a much larger number of samples and includes a measurement of color gamut as well as fidelity.
Lutron (the inventors of the dimmer) have a pretty comprehensive database. They test a lot of lights, and not all are listed. If you're buying their dimmers, call and ask if you have specific lighting pairings in mind.
We went 100% LED back in March 2014 with Philips CorePro bulbs and haven't had any issues. Either they don't have these issues, even back in 2014 (they were certainly highly regarded at the time), or perhaps my wife and I just aren't sensitive to this flickering.
Edit: Incidentally every single bulb (15 of them) is still working too, we haven't had any issues with them failing.
I have no issues with Osram Lightify GU10 bulbs (EU version), on the other hand I have proprietary fittings with Cree LEDs and Osram drivers that do flicker. So even in a single brand there can be issues...
Some cameras have slow-mo modes which try to remove lighting flicker by having a special high sample rate light sensor whose purpose is picking up the flicker and then using software to compensate the rest of the image data for the flicker pattern, using as input the time the shutter opened and closed for each row of pixels of a video frame, and integrating the light sensor value over this time.
This; state-of-the-art mobile cams should be "beating" the flicker, even in slo-mo. I'd wager the latest iphones can, although I don't have one to test.
A lot of places use fluorescent lights which will look real weird if caught in the frame without some kind of flicker compensation just as one example so its pretty important.
Uncited rumour is iPhones for the last ~3 years have had special flashlight LED's (made by NXP?) which also embed an RGB colour sensor for exactly this reason. The LED's when reverse biased send out the results of the RGB sensor. It has been suggested the reason they didn't use an extra pin was to hide this anti-flicker feature from competitors who were sure to do a detailed teardown of the phone.
With a continuous (non-flickering) light you see your blurred finger. With a flickering light, you'll see your blurred finger with gaps in the blurring. This effect is especially pronounced with sharp-flickering light (like in LEDs) as opposed to gradually-flickering light (as in incandescent bulbs). CCFLs are somewhere in the middle.
I did this during my quest to find a flicker-free LED light bulb. I found that basically all of them flicker. Some appear to alternate between banks of LEDs to reduce the dynamic range(?) of the flickering, but they all flicker. Home Depot has a rack of LED bulbs that are always turned on, so that's a good place to test many models at once.
My first thought was: why don't they just filter the output? My guess is that perhaps LEDs are more efficient when being driven full ON or OFF rather than with a steady DC.
> My first thought was: why don't they just filter the output? My guess is that perhaps LEDs are more efficient when being driven full ON or OFF rather than with a steady DC.
It's actually the opposite, efficiency goes down when current goes up.
Mine are all Brightgreen [1] high-CRI warm white downlights and they’re pretty great. They’re pretty pricy compared to the cheap no-name brands though (going for the “designer”/premium market I suppose).
'Is It Snappy?' is an iOS app that I use to diagnose whether LED bulbs are going to be shit in stores before I buy them. The IKEA bulbs have been cheap and decent.
You can also use any electronic rolling shutter with manual shutter speed - e.g. an Android phone with Camera2 API support and any of several camera apps with full manual settings. Set the shutter speed fairly high and preview or photograph the light source; flicker appears as scanlines, e.g. https://i.imgur.com/6kSoSfX.jpg.
FWIW I bought four IKEA bulbs a few years ago and all of them made a low buzzing sound. Couldn't stand them anywhere but the bathroom.
On the other hand, if you're looking for IoT light bulbs, their Tradfri system is a lot cheaper than Hue and I've read that their gateway has reasonable security practices and a good API. I would bet that those are more premium products that they wouldn't have released without making sure the electronics are quiet.
> FWIW I bought four IKEA bulbs a few years ago and all of them made a low buzzing sound. Couldn't stand them anywhere but the bathroom.
LED or CFL? The latest batch of LED's they've only had about a year, the phosphors were switched around in their 1000 lumen (lm) and 1600lm E26 bulbs. They also advertise 100lm/W.
These are not the junky dirt cheap 80lm/W 60W (800lm) equiv bulbs that you can pick up everywhere now (and I don't recommend for lighting a room).
Also, watch for open boxes, I bought ~$200 in bulbs last time and one of the globe bulbs I bought was an obvious return and did not work.
I hate lighting that flickers and will often notice it when other people do not. A few friends also notice flickering that most people don't detect. It takes tens of kHz before I won't notice a stop-motion effect like a strobe light with moving objects.
LEDs do not have to flicker, but supplying low-ripple, constant-current DC power is not as cheap as ways of powering LEDs that do result in flicker.
I rarely notice PWM strobing with most LEDs at home.
However, once place where I do notice it and it's annoying is with taillights on some cars - sometimes when I sweep my eyes across the cars ahead, I see the strobe effect from LED taillights.
It doesn't seem to happen with all cars.
I've noticed it in a few bike taillights, but not nearly as much as in cars. I used to have an early LED bike headlight, and the strobing was very apparent when the light was dimmmed, I could only use it at its highest level.
I recently walked along a road with some Christmas lights (installed by the city) with the most horrible flicker. When looking at them straight on you could just notice it, but from the corner of my eye it was really bad and distracting. I wonder if there have been any studies done on the dangers for drivers of LED flicker.
I've noticed this with the LED strip on the lower front bumper of newer Mercedes cars.
I'm pretty sure the DOT requires that your headlights don't blink, so I wonder how low the PWM frequency can be until they consider it blinking?
I also wonder whether they do it on purpose. How hard would it be to run the PWM at a few kHz instead of the < 100 Hz frequency it seems like they're using?
Tens of kHz is higher than our "normal" temporal resolution. I see crafted experiments push the critical flicker fusion rate up to almost 1KHz. You are still order of magnitude off. You should blind test that number.
That being said, obviously the fact we probably can't see 10KHz flicker, does not imply it has no effect on our well being.
In the right conditions, very high flicker frequencies can detected by humans. It doesn't require any special abilities, just the right conditions.
Consider a flickering streetlamp outside your house. Now imagine you have two sets of net curtains covering your window, 10cm apart. The net is very fine - say a 0.1mm mesh.
If you sit next to the window working, and move your head back and forth, you will see a moire effect. If you sit 10cm from the curtains and move your head at 1 m/s, the 'flashing' you see is 50 Khz. If the light source behind the curtains is flickering at 49,995 Hz, you will see the resulting 5Hz flicker when the flicker from the moire effect and the streetlamp get multiplied.
As a regular human, you have now made a 50kHz flicker detectable with no special equipment.
Flicker at high enough frequencies isn't visible directly, but only as phantom array effect with very fast eye movement and high-contrast light. Flicker fusion frequency isn't relevant. I couldn't see 10kHz flicker when I last tested it (with an LED and 555 timer), but I could see 5kHz flicker. The exact threshold will depend on the observer and the test conditions. I find high frequency flicker very annoying because the appearance and disappearance of the phantom array effect looks like unexpected motion to me, and if something is moving unexpectedly then it needs attention.
Yep, and assuming we can sweep our eyes 150 degrees in 300 ms, we get a maximum angular speed. That means that the light source flickers on and off once in (150/0.3)/10000 = 0.05 degrees. The human eye can resolve at best 0.02 degrees. This confirms the proper order of magnitude.
Edit: if you turn your head at the same time, my numbers above are too conservative.
It got even worst when shopping malls decide to follow the trend of Green Power and LED lightning while buying some absolute crap to use. The results are there are places I can't go, worst one I will feel dizzy and may want to puke, lesser ones are super annoying I don't want to go.
Problem is not everyone have this problem. I have this what I call latency intolerance syndrome.
This. I work in lighting and most of the people doing specification have never even heard of flicker. I usually get brushed off as some kind of impractical visionary.
I am on a mission to make lighting healthy. That's why I made Bedtime Bulb: https://bedtimebulb.com/ It has the lowest flicker I've ever seen in a bulb form factor—even less than those claiming to be "flicker-free."
I think you mean a secret. I'd be very surprised if you're having LEDs custom made for your application. I'll go ahead and guess it's the Nichia NVSLE21A.
I don't understand why everyone insists on bundling a transformer with each LED bulb and doesn't just make a standard for LEDs so we can buy one good transformer and then just change the LEDs when they die.
The transformers are usually less reliable than the LED's themselves.
Also, LED's unlike nearly every other electrical device are constant current devices (as opposed to constant voltage, which is what a USB port, battery, or nearly any other power supply offers for example).
Constant current devices must be wired in series rather than parallel, meaning that if you wanted more than one LED per transformer, you would need to break the existing circuit to add an extra LED. That isn't really compatible with standards around electrical plugs - you would need to short out all unused electrical outlets in a constant current system.
Constant Voltage vs Constant Current is another one of those 'DC vs AC' or 'electron has positive or negative charge' issues - We have chosen one standard, and everything is built on it. We could go back and redecide, but all infrastructure would need updating.
LEDs are not constant current devices. They are diodes with non-linear I-V characteristic curve.
The question of supplying LEDs with CC or CV power supply is only the question of efficiency and cost.
Most LED strips are made as a serial/parallel combination of LEDs with an added resistor for each segment, to get the desired current through the LEDs in a segment from a ~12V CV power supply.
You don't really have that much choice when it comes to LED strips. CC power supply would need to generate thousands of volts or you'd need a bunch of them. And that would be costly.
LEDs are better modeled as constant current because it's the I part of the curve which is typically more unreliable. The junction voltage is largely consistent, but due to the exponential increase in current, to balance the amount of power it's easier to regulate the I component of P=I*V for consistency than it is the V portion.
You can run any current through the LED. (well, up to a point :D) It's one way to regulate the brightness. I'm not sure what "modeled as constant current" really means when talking about a passive device.
If anything I simplify leds as maintaining a "constant voltage", no matter the current I send through them (in the right direction). Just like other diodes.
> it's easier to regulate the I component of P=I*V for consistency than it is the V portion.
I understand, and we're on the same page. But it doesn't change the fact that almost no led strips do this. You can iron out over individual LED differences by putting 3-4 in the series, and regulate the current using a resistor.
In fact, most of the LED indicators you'll see are driven like this. LED + resistor [+ optionally PWM or multiplexing].
Only for power LEDs you'll usually see anything more complicated invlving DC/DC CC switching power supplies.
No, I was talking about the LED light bulbs that replace incandescent light bulbs. Every one of those comes with a transformer, which we throw away when the LEDs die (or vice-versa). Could we not separate the two and have a transformer supplying constant current, and then we could swap that or the LEDs out when one died?
You don't see it directly, but you see its interaction with eye movement. See "phantom array" effect. I can see this up to at least 5kHz under the right conditions.
When there's multiple flickering LEDs in the same room, they create interference. So even if we don't notice a single one flickering, when all of them go from black to full at the same time, and this happens 20x a second, we can notice that.
While there are certainly conditions high frequencies (tens of kilohertz) can be detected by a human, this explanation isn't it.
In general, light is linear and time invariant. That means in a flickering light system, a flicker of blue light then of red light, or red and blue at the same time, are indistinguishable if the 'sampling' system doesn't have sufficient bandwidth to resolve the flicker at all.
There do exist nonlinear optical components[1], but none that exhibit nonlinearities at the light intensities you'll find at home!
Additionally, even if the above were not true, flickering LED sources tend to flicker at a multiple of the AC supply, so it's very unlikely you'd see one flickering at 1000 Hz and another at 1001 Hz for example. For battery powered devices, it could easily happen though.
Plenty of cheap LED light systems flicker at 50 or 60Hz, see elsewhere in this thread. Also, the flicker can be indirectly visible, for example by turning motion blur into a sequence of discrete strobe events. My favorite experiment is to shake the end of a spoon (because it is curved and reflective) back and forth in an area predominantly lit by strobing LEDs. You will see a number of spoons, instead of a blurry spoon like you would under incandescents.
Last year, I was contemplating bootstrapping a startup that sold full-spectrum LEDs with a controllable blue element for home and office use. Think Flux but for real lights.
I got so far as inspecting factories in Shenzhen, finding a partner supplier, and building some prototypes with my existing manufacturing contacts.
Ultimately, I ran out of time (launched another product instead) - but it always bugged me that I wasn't able to bring this product to market.
If anyone would be interested in picking up where I left off - I'd be interested in partnering.
I've used Philips Hue lights for a sort-of-flux for my office, it works fairly well. The hardware part of it seems like a solved problem with the availability of RGB smart bulbs (or the cheaper ones which only go from cold/blue-ish light to warmer orange light, without full RGB).
I use Hue at home as well. They are great for controlling blue light exposure, but the flicker (North America) and color quality leave a ton to be desired. I can occasionally see the flicker, especially in my peripheral vision.
Also, they've proven to be unreliable—I've had 4 (out of 13) suffer capacitor failure just outside of the warranty period. Their color binning is not good—new lights look totally different in color from the older ones.
I wrote about this and was interviewed on a podcast recently:
Disclosure: I sell a light bulb meant to be used in the evening before bed. It removes most of the unhealthy blue/green light, has a super high CRI, and has less flicker than "flicker-free" lighting (which could have up to 30% flicker!). Bedtime Bulb: https://bedtimebulb.com/
I had contemplated the same, though haven't gone as far as visiting factories.
As another commented mentioned, Philips Hue is a possible alternative/competitor, but unsatisfactory in some respects; precise control over exactly which LEDs light up and the lack of red LEDs in its LED array.
The goal was a fully controllable lightbulb so that blue LEDs could be turned off/reduced in the evening, and red LEDs turned on, gradually. Like you said, Flux for real light.
Correct. The goal was to have your lights automagically adjust during the day / evening, provide a gentle wakeup for winter countries / months with more blue light, and have a soft light for 3AM when you stumble to the bathroom.
I do reasonable amounts of manufacturing of other products, so had existing contacts on the ground.
The prototype build was a fully functioning strip with wifi control (and a very basic / terrible app attached).
Sticking points were marketing and bricks and mortar distributions - which are always large problems to solve.
I don't know if this applies to Hue, but did your product flicker when controlling the individual R G B color channels. I notice that with cheap gaming mice with the awful RGB LED's and it's maddening.
In The Netherlands some cyclists have this brilliant idea to put their lights on flash/flicker. I suppose some think they'll be easier to get noticed.
It is not allowed by law (the light has to be either constantly on, or it may be turned off if it isn't dark), it can trigger epilepsy, it is distracting, and it is selfish and not 'cool' at all.
It also appears to be common in PC desktops to enable all kind of LEDs, without allowing them to be disabled. Especially in all kind of colours (which Razor dubbed 'Chroma'). Not my cup of tea, a waste of aesthetic and electricity but the worst thing about it is that I pay premium for such feature because it is deemed 'cool' by the target market.
FWIW, I use a strong light in the morning to wake up. It doesn't flash.
Well, I don't like those lights either, but calling it selfish, is kinda hard when you compare it to how many cyclists get killed every year because some motorist didn't see them.
The problem being that judging the motion of a blinking light is nearly impossible. A blinking light is both more attention grabbing and less safe for the user.
In an urban environment there will usually be more than enough light to see and predict the course of a cyclist. The trick is attracting the attention of people that are not looking in the first place. Flashing lights work very well for stimulating peripheral vision in a moving visual field.
> I wonder what you think of emergency sirens/lights? Too distracting?
If unnecessary, yes.
> Distracting drivers from what, exactly?
> Distracting them from not seeing cyclists?
We only have a finite attention span; hence such is going to be distracting the driver from other important things on the road. Not every cyclist is so important to be noticed.
You should also take into account that a blinking light means the driver is changing lane or course. Two blinking light means danger. If every bicyclist would all the time be signalling "danger, danger", people become desensitised to such signal.
Excuse me for keeping my flashing lights on the bike when there's people with attitudes like yours controlling several ton killing machines within meters of me.
This is something that should really be solved by regulating bicycle lights sold, or a very broad public awareness campaign.
These cheap Chinese LED lights for the bicycle all come with a blink-setting, and like the <blink>-tag of yore, it serves no practical purpose. People tend to think blinking means you are easier to spot in the dark, which is true in the sense that it grabs attention, but as you mention, you can't really extrapolate where someone is going with a blinking light.
The use of the blinking setting is usually born from naivety. People use the setting, because it is included with the light — why else would it be there, if not to use it? Now imagine if every cyclist on a busy cycleway used the blink-setting. At that point this behaviour is downright selfish.
It's not too hard to regulate really. After all, you are already legally limited in what you can use (white/yellow front, red back, no blinking).
There are quite a lot of these in the UK too, again I'm not sure of the legality.
As a driver I've two things to say about them.
Firstly, they do make it easier to spot the cyclist over a solid light so that's a good thing. However, it's almost impossible to track their movement and that is a very very bad thing.
The best solution I feel is to have a flashing light which draws attention in addition to a solid light which is much easier to keep track of in your peripheral.
The rules in the UK have changed somewhat over the years; it used to be that flashing lights were only permitted in addition to a constant lamp.
Now its fine to only use flashing lights - Rule 60 of the highway code:
"At night your cycle MUST have white front and red rear lights lit. It MUST also be fitted with a red rear reflector (and amber pedal reflectors, if manufactured after 1/10/85). White front reflectors and spoke reflectors will also help you to be seen. Flashing lights are permitted but it is recommended that cyclists who are riding in areas without street lighting use a steady front lamp."
With the insane brightness now possible I wish they had to meet the same light pattern rules car headlights do. I think that would help the flashing being so distracting.
A very bright bike light makes it much more comfortable to ride a bike at night, you need to compete with car headlights so that you can see the surface of the road in front of you. Cars don't need to worry about the road conditions as much as cyclists since if they hit a pothole or a stick, it's no big deal.
I'm hoping cars (and bikes) evolve over the next few years into less blinding headlights. The infatuation we have with projectors makes even halogen lights blinding. I see some newer Acuras coming with multiple LED projectors on each side lately, which ought to help (so long as overall output is constant, and each projector is dimmer)
Really good point. It's worth noting that the bikes belonging to our official bikeshare here in NYC all have blinking white lights on the front and solid red ones on the back. You'd think a bike share would be able to get this right. Maybe they should have both blinking and solid ones in both places.
Blinking lights save power and lead to longer battery life, hence the cycle lights with different blink settings. The power savings can be substantial, one of the back lights I use switches between 'full on' (3 leds, full power) and 'walking blink' (¼ second on/off). Subtract the (negligible) power used by the timer IC and you end up with a factor 6 difference in favour of the blinking light. Here in Sweden blinking lights are still allowed, one of the places where you'll meet them is on the railroad as Swedish trains have blinking back lights.
Blinking headlights on bicycles are not allowed in Sweden. (It's hard to argue with the market forces of millions little LED lamps though, combined with disregard or not knowing about the law.)
Headlights, no. Blinking taillights are allowed though (with a minimum blink frequency of ~3.3 Hz / 200 per minute) and those are the ones I mentioned. Blinking taillights do make bicycles stand out more which can only help in a country like Sweden where cycle paths are as rare as hen's teeth. In the Netherlands (where I'm from originally) this is less urgent as there are plenty of cycle paths.
Flashing bike lights are ubiquitous in the United States. I prefer them because I can distinguish a cyclist from what could be a slow car missing a tail light.
Here in the south of Spain I regularly see scooters (mopeds) that are 20+ years old. Older scooters often have headlights that are so dim you can barely see them (the bulbs just get dimmer, they don't burn out). As a car driver I'd much prefer to see a bright and flashing light so I notice the vehicle, and a bicycle doesn't make any noise so I'm not going to hear it.
> Flashing lights will be perceived as having higher brightness than steady-burning lights, up to a flash frequency of about 15 flashes per second. Such brightness enhancement can aid in conspicuity, and several rear lighting systems have been designed to have a flash rate between 5 and 9 flashes per second in order to maximize their perceived brightness.
I think deep down we all know this anyway, which is why we want flashing lights if we are on a bike amongst traffic. Why on earth would emergency vehicles and maintenance vehicles use flashing lights if they were equally effective to steady lighting?
Your daughter's bike would be far more noticeable with flashing lights.
That paper is about rear lights on snowmobiles, in snow (in upstate New York). My daughter doesn't have blinking lights on the back of her snowmobile. It barely even snows here. If it snows, the roads can be dangerous for bicyclists due to weather conditions. I'd rather bring her to school myself in such a situation, or buy her public transport instead.
Blinking lights in traffic serve to warn us about danger. Bicyclists are just normal cyclists; so the other users of traffic get warning fatigue via your method. A reflector (legally required to be on a bicycle on the back) is going to adequately help them. As a runner, I also wear clothes which contain reflections.
I think the general idea that flashing is more noticeable than steady can be taken from the paper. Seems like common sense to me.
I'm a cyclist and I'll stick with my flashing lights, thanks. I have steady lights as well so drivers can track my motion.
Whatever it takes for those oblivious and distracted SUV idiots to actually notice that I'm there. I've had a few very close calls already, I guess those poor long-suffering drivers must have had warning fatigue. /s
I'm a driver as well and I don't find flashing lights on bikes very distracting while driving. What's much worse are the cyclists with no lights, which makes it difficult to judge their position, or even to notice their existence at all.
You have a much greater need on a bike to see road detail, you need to look out for potholes and sticks on the road. In a car, you just need to be able to see the road lines and reflect light off of signs.
I use a 1200 lumen bike light, powered by two 3500mah 18650s.
That's great for you, now imagine the guy coming the opposite direction being blasted with 1200 lumen in the eyes. Sure you made him aware of your presence but you also made him blind to any other stuff or people besides you.
If you find blinking lights on cyclists annoying, that means you noticed them. So they accomplish their mission. Blinking lights are significantly easier to notice from peripheral vision.
>Seeing something is not the same as having enough information about that thing to avoid an accident.
I'm really confused by this thinking. If there is a blinking white light pointed at you it means the cyclist is on the other side of the road, traveling with traffic in the opposite direction. If it is blinking red then you are approaching the cyclist traveling in the same direction as you, on your side of the road. If you see both lights blinking, with the white light on the left, then the bike is traveling left across your direction of travel. White on the right for the opposite. What information am I missing here? I feel like any of these combinations should be enough for a driver to notice a cyclist and to give them a sufficiently wide berth.
> If there is a blinking white light pointed at you it means the cyclist is on the other side of the road, traveling with traffic in the opposite direction.
Do drivers know this? Or do they think the flashing light is something else? Do they even see the flashing light? It's possible that eye movement across a scene means the eye travels over the cyclist in the off-time of the light.
You're saying "don't see them at all", but we don't know if that's what happens. We don't know that drivers don't see fixed lights, or see flashing lights more often. And we don't know what information they get from the lights.
This should be flagged, tagged, or somehow made to be seen by new vistors to the site, as I had to track this down to figure out what this site was even on about.
I was impressed by how fast and uncluttered this site is. In case someone else is wondering: It seems to be running https://flarum.org/, a PHP forum with a Mithril JS front-end
But it's terrible for search, both internal and external(Google).
Why ?
Let's start with internal search. Ctrl-f fails in thread search. No other mechanism to search inside a thread.
And about external search:
Permalinks to individual comments - great for the search engine when you request a very specific thing - a specific niche comment from this site could get ranked highly in google.
Also, it's making it easy to link to a great comment is import. Impossible here.
Permalinks to webpages that contain full threads - lots of relevant text for the search engine to chew on. But in flarum the content lazily loads. So maybe Google wouldn't be able to chew on all the comments.
And the fact that when Google finds a thread from the site, he doesn't say how many comments per thread , indicates that he doesn't see this as a forum, which could be bad
And all this is a real shame - it's a community with really valuable content.
It's also new forum software (I'm developing it), sort of a combination of Discourse and HN and Slack. I would think it works ok with external search? Becasue, like here at HN, good comments surface to the top, + they're included in the HTMl directly on page load. So, what a search engine sees, ought to be the original post, + the best comments.
I'm wondering, what do you mean with: "Also, it's making it easy to link to a great comment is import"? (What does "import" mean, here)
1. the way you do permlinks to individual posts looks good. It's also easily shareable. good too.
2. but probably, an even better way to do permalinks is something like quora did - just the specific answer that solves the user's problem , in a seperate non-distracting page, with a full, human readable url.
That of course creates a problem with sub-comments, but quora solved it nicely by hiding them .
3. Content quality is key for SEO. Assuming that upvotes works well for that. i don't know much about forum design, but i assume upvotes are really sensitive to the community and that's why HN is so great.
but in other communities, i wish there was a way to sense if "this answer solved the issue" or something similar, and letting that rise. That's probably one of the reasons stackoverflow won.
But forums are somewhat different so that's harder.
4. Adding that "recommended links" on the site could help SEO. but it's a shitty user experience. So probably isn't worth it.
Thanks for the feedback. Interesting to see how Quora does answer permalinks. At the same time, then other answers, aren't easily discoverable.
Yea, upvotes only work, if the community "collectively" has a good judgement :- ) Also, I'm thinking about weighting upvotes, with how good a judgement the voter seems to have, based on trust levels and fraction upvoted and downvoted answers, hmm. So a staff user's or a trusted core member's upvotes, have a bit more weight, than votes from a new and unknown person.
Perhaps it's the subject matter that has driven the site design towards a paler pastel colour palette, but I find it quite pleasing to the eye.
Although I do wonder about accessibility. Some of the lighter colours don't pass WCAG recommendations for contrast. But it's rare to find a website outside of gov.uk that even comes close.
Let me shed some light on how you can drive LEDs from an AC power source. Naturally the worst techniques are usually the cheapest. To add to the complexity, directives like EnergyStar are aiming for power factor >0.9 in lighting above 3W. Maintaining high power factor (sin^2 input power) while having low lighting ripple (constant output power) requires some method of of storing energy. In methods 1,2,3 (and 4 depending), neither high power factor nor good lighting ripple is achieved, but very low cost is.
Note that this info is for fairly low power LEDs. When you start having high power LEDs, regulations may require better power electronics, and the cost of the electronics might be amortized against the cost of the thermal cooling solution, etc, so you can make a more expensive electronics package.
1) By stringing ~ 180v of LEDs in series, and adding a current limiting resistor, you can drive the whole thing from the AC line. This has terrible variability (short light spikes every 60hz, and the thermal effects will change the LED properties so much that you could easily have 2x light intensity change as they warm up) and poor total illumination (as most of the cycle is spent with the AC waveform lower than the needed voltage. I haven't seen this in the wild, as option 2 isn't much more expensive and far better.
2) Use a single diode + capacitor rectifier to generate ~180v, and then have a similar string as in (1). This gives far better illumination (the capacitor will probably stay in the 160-180v range), but still has substantial 50/60hz ripple based on the size of the capacitor
3) Similar to (2) but use a full bridge rectifier instead of a single diode. As we are now driven by a rectified sine wave, the ripple voltage will ~half, and the ripple frequency will now be 100/120hz.
4) Many applications don't have ~60 LEDs in series, so you can't drive directly from the rectified AC line. The first stage is a rectifier, and a second stage most likely is a buck converter. The quality of the light out of this depends on how much you care about power factor. Chips like NCL30288, for example, maintain high power factor and fairly low lighting ripple. Most people won't notice this.
5) Particularly in higher power lighting, a separate power factor correcting stage achieves high power factor, and a second stage generates a constant current that should have exceptionally low luminous intensity ripple (if designed right). The ripple frequency should be in the hundreds of kHz as well, so I don't think any eye could notice this.
And don't get started on dimming, I haven't found a product on the market that does non-phase cut dimming in <20W lights.
6) use any of the above methods but with UV leds and coat the glass on your bulb with phosphor, giving some extra buffer to the flicker by way of a slow brightness decay.
I'm fairly sure the IKEA bulbs use the above method. If you turn them off they have an afterglow for a couple seconds.
There's also the "capacitor dropper" method that uses a capacitor as a frequency-dependent resistor and has a slightly better efficiency but lower power factor than a resistor.
Thank you, very informative on how low cost low power LED is achieved.
It seemed like magic at first but after reading your comment it is more like dark art.
One interesting use for flickering LEDs is to help figure out the readout speed and clock rate of a digital camera sensor by exploiting the rolling shutter. Some discussion and experiments on this technique can be found here: https://www.magiclantern.fm/forum/index.php?topic=23040.0
Tis the season for PWM-induced headaches from cheap LED Christmas lights.
I'm curious if folks in countries with 50Hz mains have the same issue. At that point it might be so bad that products without at least a full bridge rectifier would be unsellable.
Many xmas lights flicker, even when they're not in blinking mode. With the really crappy ones it's often noticeable just by looking at them. With some of the slightly less crappy ones, it's easier to notice when looking at them out of the corner of your eye.
Being aware of LED flicker and having been to places with both 50 Hz and 60 Hz AC, the places with 50 Hz are definitely worse. Extremely easy to perceive. Plus, it can be difficult to take photos under this light.
Also, most of the "Edison-style" LED bulbs on the market use really cheap drivers. This is especially true outside the U.S. where you can get an LED "filament" with integrated half-wave rectifier. Thankfully UL is not allowing this crap in the U.S., but Edison-style LEDs here still (mostly) use very cheap driver topology.
I'm on a mission to make lighting healthy. That's why I launched Bedtime Bulb: https://bedtimebulb.com/ We have the lowest flicker of any bulb I have ever seen, even less than those claiming to be "flicker-free."
Interesting. Reading some of the comments they really run the gamut (no pun intended). It's reassuring to see though that people are starting to pay attention to this. For myself, it is the flicker (PWM) of some LED drivers that I am uncomfortable with. I went through a few different brands of LED track lights before finding one where I could perceive no flicker.
Similarly for LED lightning in the garage.
For the kitchen I had a need for rope lighting and never did find LED/driver combo that I was happy with.
Here's a trick that I've found useful: If you have a phone that can do slow motion capture (I have a Pixel 2, but this also works with an iPhone), go to a Home Depot or Lowe's and take a slo-mo (240fps) video of the LED bulbs they have on display. Most flicker horribly on playback, including the expensive Cree bulbs.
The built-in LED spotlights that came with my house flicker like a rave concert whenever I capture a video in slo-mo. It's unsettling.
Phillips LEDs, especially the Scene Switch bulbs, are flicker-free according to my tests. Surprisingly, older CFL bulbs flicker much less than LEDs.
Trying this at my house I don't see flicker from either my Philips warm glow bulbs, my Luminus Elite bulbs from Costco, or my Philips Hue lightstrips, but do see flicker with my Philips Hue A19 bulbs.
Former product display engineer here. Many of those light bulb displays are only meant to demonstrate color temperature, and have completely different power systems on board then an actual light bulb. Usually the AC rectification will be removed and replaced with a DC/DC converter.
This is mostly so that the display can be battery powered, because the availability of AC power on shelf is pretty hit or miss. I wouldn’t trust a display to indicate if the bulb has flicker or not.
The ones you're talking about demonstrate color temperature. The ones I've seen demonstrate the different light output of different brands and are connected to AC through a dimmer. You can play with the dimmer, and the price of the dimmer (each dimmer is different) and the bulb are displayed.
I can't imagine those are battery powered or that every different bulb on display has been modified.
Well, if its a light in your house, it is within your control. What if it is at work? In the public transport? On the street? In a grocery store? At a customer? If you suffer from LED strain, it'll hamper your ability to function in society. All this reminds me a bit of Chuck in Better Call Saul (portrayed by Michael McKean). Regardless of what he exactly had, the man was ill.
This is not that. This is multiplexing and the purpose of it is to save i/o wires. If you film it with a high speed camera you will see something like one digit being lit at a time.
This is interesting. If LED lights pulse so quickly that we don't notice the flashing, how are these people able to perceive it in a way that causes them pain?
1) I think it is totally possible that small scale effects can bug you at different layers of your neural processing: just because it is extremely difficult for me to perceive a sound doesn't mean my ears aren't being affected by it and even providing a signal to my brain with the information where it is being discarded actively.
2) They often don't? A lot of LEDs flicker at something like 60Hz. Sure: if you stare at the light you might not notice it blinking, due to the limitations of the sensors in your eyes that can weirdly "get tired" of looking at the same thing for too long, but if you move your eyes across the light quickly you will see it blinking as now you are getting a broken dotted line carved into your vision. I find this maddening when there are such lights in my peripheral vision.
Different parts of your eye are attuned to different frequency responses. For me, it is easier to see flicker in my peripheral vision rather than my direct vision, so if something is off to the side it can be more annoying than something right in front of me.
That said, I can eliminate all annoying flicker by making sure that all of the things that flicker aren't mixing down into ranges that start to annoy me. For example if you have some LEDs that are running at 15Khz and some that are running at 15.1Khz they can set up a beat frequency at 100Hz that is annoying. I had some dimmable can lights that did this and figured out that the PWM was local oscillator based (R/C if you can believe it) rather than crystal based. I found lights that used the line frequency to drive their oscillator so they are essentially all in sync (at 2.4KHz or so, so not noticeable to my eyes)
Back when DLP projection TV's were popular, I used to see the "rainbow effect" and it was distracting enough that it was hard to watch anything on the TV.
Many people can see it, but don't really notice it... until you point it out. I pointed it out to one guy that owned his TV for a year and never noticed it, but after I pointed it out to him, he couldn't stop seeing it and could never enjoy his TV after that.
From my personal anecdata, they don't perceive the LED flashing directly. Objects in motion look weird under some LED lighting. Motion doesn't look smooth. It's like a weaker version of looking at moving objects under continuous camera flashes. The effect isn't super explicit, but moving objects become jerky. Try looking at a fan under the lighting of cheap Christmas LEDs.
More sensitive people will notice this effect even at a few kHz when an object lit by the source moves quickly or the viewer's vision pans across the light source. Even faster PWM up to a few kHz is visible to some people this way.
Everyone can see the flashing. You can become aware with a bit of effort.
Find a LED light that isn't on a continuous DC power supply. Christmas lights work well for this.
Pick two objects, one far to the left of the light, one far to the right. Focus on one side, while making sure the other object and the light remain in your field of view. Next, glance at the second object so your eyes quickly travel across the LED.
If you have christmas lights you can exaggerate the effect by spinning the cable. You don't need to move your eyes at all in that case.
If you have manual control over the shutter speed on a smartphone or other electronic rolling shutter camera, just turn the shutter speed high. It's possible to detect flicker up to at least a few kHz this way.
The pain just comes regardless of whether or not you actually perceive why. For me it's kind of a cramping sensation at the back of my eyes and if there is no other light source (think christmas tree with cheap LED lights in an otherwise dark room) i will also get nauseous.
If you're shifting your view/moving your head you can easily perceive the flashes.
You can't see UV light, but if bright UV light shines into your eyes it can make you blind. You don't need to be able to consciously perceive something for it to have a physiological effect on you.
I noticed that with some tvs if I look at something else I can see them flickering in the side of my vision but if I look directly at them they look fine.
I Learned that if low freq LED flicker strains your eyes, then there's a chance you'll feel discomfort from emerging display HDR color dithering as well. For example, if the panel is 8bit but it shows you 10bit color space by 8 bit plus A-FRC.
Bought a 2018 Macbook pro and it produces similar symptoms like years ago when I had a laptop with bad low freq LED backlight.
Right now using a late 2010 and a 2013 Macbook Pro both with native screens and on external screens and it does not make my head hurt. 2018 one strains me both on native screen and on my otherwise good daily driver BenQ monitor.
Related Question: Is it possible for AM-OLED to be PWM free? ( Apart from setting it at maximum brightness ). Or would we have to stick to this until MicroLED comes.... which is still years away.
Edit: I know W-OLED used by LG does not have PWM problem, but that is not for mobile uses.
In summary they are saying that low frequency (240Hz) PWM is used for amoled because it decreases sub-pixel wear, it prevents color distortion, it's cheaper. So it looks like this won't change. I got an amoled phone and was surprised that the experience was worse than LCD (for me - it seems to depend a lot on the individual). Didn't even know that PWM was used until I started googling eystrain and amoled. Anyway, I sent the phone back.
Check notebookcheck's reviews to find AMOLED phones that eiter don't use PWM (I think it's only about 2 of them) or only use it above a certain brightness level. For example, the Axon 7 Mini. It seems those displays started to show up at around 2016.
A small 60 Hz flicker will remain though, similar to as seen on OLED TVs.
I'm sensitive to this flickering as well. Cars in motion, traffic lights, destination/passenger information displays, POS, sometimes ATMs. Though the "car-thing" mostly faded away over the last few years. They seem to got that right now. Anyways, i tried some of them over the last decade and they were all trash, made bad light, needed time to warm up, had coil whine or buzzing and broke after a few months. Then in May this year i tried some again and they were absolutely OK. It's called "LED-Retrofit" which means it fits in old sockets, based on this technology:
https://en.wikipedia.org/wiki/LED_filament
No dimming, no "smarts", no color/ambilight etc. Just works as it should. Mine are from Osram, for something like 6 to 12 Euros a piece, directly plugged into E27/E14 sockets at 230V@50Hz. And most importantly no ugly interactions with my screens running at 60Hz. This reminds me of scissors, for a long time they needed to be resharpened. Then, since maybe two, or at least one decade ago you could get good and f......g dangerous scissors which cut through almost anything whitout getting blunt/dull for next to nothing.
Now seems to be the point in time where this happened for LED-lighting. At least when it's based on this "LED-Filament"-thing. HTH.
Sure, when the AC is on in late spring/summer, LED makes a heck of a lot more sense. But when the heat is on, filament lightbulbs serve as space heaters as well as glowy-warm lights.
And with the whole open question of blue light and retinopathy, tells me that until this is resolved that again, incandescents are better than LEDs. I already knew that those damned 'blue LEDs' are painful at night. I now know why.
As someone who suffers from this since the arrival of LED backlighting, I wonder if there are lighting technologies on their way that will eliminate the issue?
Correct, OLED doesn't use backlighting, but the problem is the PWM used to dim pixels, which is also used on OLED displays. I haven't tested the difference, but I've read that for others OLED in and of itself doesn't help.
Built-in converters for retro fit are such a waste. An external converter is small enough to build into the enclosure and industrial setups do just that.
1. Lots of LEDs flicker. Shitty ones with twice the frequency of the main current (so 100/120 Hz) While you might not notice this it causes eye strain and can lead to eye fatigue, headaches, migraines.
2. Most LEDs have a low CRI (Color Rendering Index, or called Ra which is one standard to measure it), this means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% of a spectrum that covers most of the visible light.
If you look around you'll be able to find reasonably priced LEDs with 90+ Ra and no flicker, but its a pain in the ass to research it. Especially if you need something more special like a LED light strip for your kitchen.