Photoperiods are a critical component of maintaining the animal's environment. Therefore, automatic control of lighting in windowless animal rooms is the norm. Most research facilities will require independent lighting control for each animal room. Conventional fluorescent lighting is standard for animal rooms. The ceiling fixtures may be recessed or surface mounted. The light fixtures should be water resistant and arranged to provide uniform lighting throughout the room. A digital light control system located in a secure location remote from the animal rooms is best. A dark room light independently controlled with a timer switch at the room may be used to facilitate activities that must be conducted during the dark cycle.

High light levels cause retinal damage in albino rodents. In recognition of this phototoxic effect, the ILAR Guide4 recommends that light levels in rooms housing albino animals be 325 lux (30 fc), 1 m

(3.3 ft) above the floor. This level is generally sufficient for animal care, and task lighting can be provided for performing procedures that require higher levels of light. A bilevel low/high (325 lux/800 lux) lighting system may be considered with the intent of using the high level to facilitate working in the animal room; however, it must be noted that even brief periods of high light levels may result in retinal damage for albino animals. Retinal damage does not occur in animals with normally pigmented eyes at typical indoor lighting levels. Therefore, it is acceptable and even desirable to provide light levels of 800 to 1100 lux (75 to 100 fc) in animal rooms designed to house only dogs, nonhuman primates, or other animals that normally have pigmented eyes.

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