Abstract Disclosure: A.M. Yaw: None. M.E. Gardella: None. J. Jacobs: None. H.M. Hoffmann: None. Millions of cats enter animal shelters each year. Unfortunately, due to high numbers of cats entering shelters and limited physical housing space, over 50% of healthy and adoptable cats with extended shelter stays are euthanized yearly. While animal shelters are essential for keeping cats safe from unfit living conditions, they are a stressful environment. High stress in cats increases health risks and undesirable behaviors and is associated with reduced adoptions. Given the role of light in regulating hormonal stress responses and behavior, we partnered with a Midwestern animal control and shelter to evaluate how light intensity and light composition impact feline behavior and urinary cortisol levels in 123 domestic cats (Felis catus; 65 male and 58 female). The impact of three lighting conditions, white, dim, and orange (blue-depleted) light, were evaluated for the first 5-6 days following admittance into the shelter. Individually housed adults (8 months-10 years) were outfitted with PetPace Smart Collars to evaluate locomotor activity, and cat stress was evaluated daily through urine samples and a behavioral approach test. All data were analyzed by experimenters who were blind to the groups and tested via one or two-way ANOVA or repeated measures mixed-effects model with Geisser-Greenhouse correction. Urinary cortisol levels were dependent on both light quality and day in shelter, where cats under orange light had reduced cortisol on days 4-5 in the shelter compared to cats in standard lighting. Light quality also altered cat hiding behavior, such that the percentage of cats hiding was increased on dim light compared to both standard and orange light. A novel behavioral approach task found reduced cat stress on days 4-5 in standard and orange light; however, dim light increased cat stress on day 5 in shelter. All cats exhibited circadian rhythms in locomotor activity with periods ranging from 21.33-35.67h independent of light condition and day in shelter, and locomotor activity increased on days 3-4 compared to day 2 in the shelter, with no effect of light condition. There were no sex differences in in hiding, PetPace activity, or cat stress scores under any light condition; however, females displayed increased urinary cortisol levels compared to males in standard, but not dim or orange, light. This shows for the first time that room light manipulation can help shelters enact easy and inexpensive changes that make the adjustment period shorter and less stressful for incoming cats which will improve animal wellbeing. Presentation: 6/1/2024