By providing light to the mitochondria, an LED treatment "triggers biochemical reactions that ultimately lead to beneficial effects on the skin, such as fibroblast proliferation and collagen production," Dr. Park explains. It depends on the light color—the most commonly used lights in LED devices are red, infrared (which can’t be detected by the human eye but is felt as heat), and blue. And for LED light devices in particular, you should skip them if you have "a seizure disorder, epilepsy, or a condition that causes sensitivity to light like lupus or migraines triggered by light," says Dr. Park.