> We used two types of lighting devices. For exposure to white LED, commercial cold white LED panel generating 2300 lumens during 24 h was used. The LED panel was placed above 8 transparent cages, placed on white surfaces, leaving enough space for air circulation and constant temperature maintenance at 21 °C. The illuminance measured at the rats’ eyes position was 6000 lux (Photometre DT-8809A, CEM, China).
> For long-term exposure, specific devices were built and characterized by Statice, France (Fig. 1A). Metallic boxes contained rows of LED with a diffuser in order to improve the directional uniformity of the radiation and avoid punctate sources. Alternatively, CCFL or CFL were uniformly distributed around the metal cages. Each cage was placed in a metallic device that was then placed in a ventilated cupboard allowing for a constant 21 °C temperature control (Fig. 1A). The light intensity was controllable and the distribution of light in the cage was homogenous whatever the rat position. Different types of LEDs were used: cold-white LED (pure white 6300 K), blue LED (royal blue 455–465 nm), and green LED (520–35 nm) (Z-power LED, Seoul Semiconductor, Korea). Exposure intensity was spectrophotometrically measured by Statice.
> Exposure protocols
> Acute exposure: LE and W rats were maintained in a cyclic light/dark (250 lux, 12 h/12 h) environment for 21 days. The day before light exposure, rats were dark-adapted for 16 h. The next day, pupils were dilated with 1% atropine (Alcon, Norvartis, Rueil Malmaison, France) under dim light, and rats were isolated in separate cages containing enough food for one day. After 24 h of exposure, rats were placed again in a cyclic light/dark (250 lux, 12 h/12 h) environment for 7 days and sacrificed for histology and immunofluorescence analysis. Control rats were submitted to the same pre conditioning protocol but not exposed to light. Different types of light sources and light intensities were used as detailed in Fig. 1B. For cold-white LED, different light intensities were tested from 6000 lux, to 1500, 1000 and 500 lux. Blue and green LEDs were used at 500 lux which is the domestic classic light intensity. CFL was used at 6000 lux and 500 lux, CCFL at 6000 lux. Illuminance was measured at the level of the rat eye.
> Long-term exposures: Rats (LE and W) were maintained in a cyclic light/dark (250 lux, 12 h/12 h) environment for 21 days, then placed in specific cages for chronic cyclic exposure to different types of light at 500 lux: CFL, white, green and blue LEDs. Animals were sacrificed right after 8 or 28 days of exposure. For the long-term protocol and in order to be as close to domestic light as possible, rat pupils were not dilated.
This sort of thing should have had 2 control groups. One kept in the dark, the other exposed to the light protocol they used for artificial lighting, using natural sunlight as the light source.
Its not clear from the wording above exactly how the control group was exposed in pre conditioning, and what the nature of their post exposure protocol was.
500 lux in cyclic test is not outside the realm of reason for representative real world exposure.
Personally, I'd like to see a control under natural sunlight, and one under a man-made filtered blackbody radiator.