Can darker window tints reduce interior light impacts to hatchling sea turtles on developed coastlines? An experimental assessment

Coastal light pollution is a global threat to hatchling sea turtles and a leading cause of mortality, particularly in urbanized areas. Although lighting regulations can reduce hatchling exposure to disruptive exterior lighting, interior lighting often is not addressed. Florida, USA, is one area with state regulations specific to interior light, requiring beachfront properties to use glass with a maximum visible light transmittance (VLT) of 45% to reduce interior light visible from the beach. Yet reports of hatchling disorientation events in Florida regularly implicate interior lighting. We conducted 400 y-maze assays with loggerhead (Caretta caretta) hatchlings to investigate whether glass with a VLT lower than the current industry standard of 45% would reduce hatchling attraction to interior lights. During the assays, we presented hatchlings with full-spectrum white lights shielded by various tinted glass samples and allowed them to choose between a 44% VLT control glass and other samples of glass ranging in VLT from 15% to 41%. We found a significant positive relationship between a higher VLT and the likelihood of hatchlings orienting toward the test sample, with hatchlings exhibiting less attraction to samples with a lower VLT. Hatchlings responded similarly to the control sample and to those with a VLT above 30% but were less likely to choose samples below 30% VLT. Our results suggest that glass with a VLT of 30% or lower could reduce hatchling attraction to white interior lights compared to the current coastal construction industry standard of 45% VLT glass.