Figure 4. Different light treatments did not affect rhodopsin mRNA levels (one-way ANOVA, p>0.1). Exposure to blue light (λ_max 474) at the intensity of 1×10⁻¹ μW/cm² for 4 h/day for 30 days produced significant changes in the mRNA levels of short wavelength sensitive (SW) opsin, melanopsin, and medium wavelength sensitive opsin (* one-way ANOVA followed by Holm-Sidak tests, p<0.05). Rats were exposed to blue, green, or white light-emitting diodes (LEDs) every day (4 h) for 30 days in the middle of the day (11:00 to 15:00) and then returned to a 12 h:12 h light-dark cycle. The intensity of the light during the light phase of the 12 h:12 h light-dark cycle was about 400–450 lux. Every day, the pupils were dilated with 1% atropine and 2.5% phenylephrine eye drops 45 min before exposure to blue, green, or white light-emitting diodes (LEDs). After 30 days, the rats were killed, and the retinas were explanted, immediately frozen, and stored at −80 °C. mRNA was then extracted, and mRNA levels were measured using real-time quantitative PCR (qPCR; see [122] for details about primers and qPCR conditions).