Which of the following is a true statement about room illumination for rodents?

• A. Lighting should be uniform with no dark period
• B. The room should have daylight cycles that never reach darkness
• C. Lighting should have a 12:12 light-dark cycle
• D. Illumination does not affect welfare

Answer: (C)

Regular light-dark cycles support the circadian rhythms that rodents rely on to regulate activity, feeding, and physiology. A 12:12 light-dark cycle provides 12 hours of light for activity and 12 hours of darkness for rest, aligning with natural patterns and promoting normal behavior, sleep, and overall welfare. Continuous light or never reaching darkness disrupts entrainment, increases stress, and can negatively affect growth, reproduction, and immune function. A regime that never includes a dark period also prevents essential rest and harms welfare. Illumination clearly affects welfare, so a 12:12 cycle is the recommended standard; keep the dark phase genuinely dark and avoid light leaks during the night.