“Photoreceptors are like the vehicle. Retinal is the gas,” says study author and chemistry professor Ajith Karunarathne. In the lab, when cells were exposed to blue light directly—in theory, mimicking what happens when we stare at our phone or computer screens—the high-intensity waves trigger a chemical reaction in retinal molecules. The blue light causes the retinal to oxidize, creating “toxic chemical species,” according to Karunarathne. The retinal, energized by this particular band of light, kills cells, which do not grow back once they are damaged. If retinal is the gas, Karunarathne says, then blue light is a dangerous spark.