For comparison, typical artificial light levels in an office are more like 300 lux. IES recommended illuminance for a professional indoor basketball court is 1000 lux.
Daylight ranges up to 120,000 lux, so 6000 is several times the lighting in most spaces, but still nowhere near bright sunlight.
That said, from the abstract (I don't have journal access), it sounds like they found a result in both 24H high intensity, and in on/off "domestic levels".
Is the 6000 lux you mentioned their value for high intensity, or is that what they considered as domestic levels?
multiple experiments were made, one at 6000 as the GP mentions, but also one at 500 lux. There's more information here but in French[1][2]:
On the other hand, by exposing the same animals to a luminous intensity similar to that usually used in dwellings (500 lux) for 24 hours, only the LEDs appeared harmful
500 lux is also much greater than what reaches your eyes in a typical household lighting scenario. If you stare in to a 100W incandescent light bulb from one meter, you're getting about 100 lux to your eyes.
We don't usually stare at light sources; we use them to illuminate objects. A 100W incandescent from 1 meter on to reading material or other work is considered fairly brightly lit, and that's not getting the full 100 lux back to your eyes - only what the surface reflects.
Daylight is far brighter, but most of us have been warned from early childhood about the danger of staring at the sun. 100,000 lux may be present, but we're not directing it in to our eyes.
Daylight ranges up to 120,000 lux, so 6000 is several times the lighting in most spaces, but still nowhere near bright sunlight.
That said, from the abstract (I don't have journal access), it sounds like they found a result in both 24H high intensity, and in on/off "domestic levels".
Is the 6000 lux you mentioned their value for high intensity, or is that what they considered as domestic levels?