The Future Is Not Bright: Evaluation of Rat Preferences for Color and Intensity of Light.

Light is a key factor influencing the welfare of laboratory rodents, but little is known about their optimal lighting condition. It i common knowledge that rats prefer dim light, so bright light is mitigated with red-tinted shelters or cages, which alter both the color and intensity of light. Because both aspects are altered, the contribution of each feature to rodent preference is unknown. Further, it is unknown if this preference is influenced by previous experience. We hypothesized that rats would prefer lower light intensity and that their preferences would be influenced by their housing environment. Breeder pairs of rats were randomly separated into four treatments groups: red 200 lux, red 25 lux, clear 200 lux, and clear 25 lux. The breeders' offspring were tested three times in an apparatus that offered access to each environment, and their preferences were analyzed. Generally, the rats preferred the lower-lux environments and showed no color preference. However, the rats from the clear, 200 lux cages, preferred clear caging and only showed a preference for 25 lux conditions during the second and third preference tests. These results suggest that the light intensity, more than color, should be considered when designing rodent housing and testing facilities.