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
[1] https://translate.google.com/translate?sl=fr&tl=en&js=y&prev...
[2] http://www.inserm.fr/actualites/rubriques/actualites-recherc...