None that have been observed. This is important, so allow us a moment to talk some science to reinforce that statement. The millisecond light pulses technology incorporated in the Lumos Smart Sleep Mask has been tested on people across multiple studies at the Stanford Sleep Lab, and no known negative side effects have been observed in human use to this point (see studies below). The light intensity from Lumos Smart Sleep Mask is orders of magnitude lower than the intensity of light a human eye will be exposed to doing normal activities during a normal sunny day, and the pulse frequency orders of magnitude less than the frequency that can induce seizure and epilepsy.
Despite the safety evidence from lab studies, we recommend that users who are on non-sleep medication or suffering from any sort of serious medical conditions check with their doctor before using the Lumos Smart Sleep Mask, and discontinue use if experiencing any sort of adverse reactions such as dizziness or migraines.