There are a few different causes of seeing bright colored spots. Seeing a spot is basically a sign that the retina of the eye (the light sensing part of the eye) is being mechanically or electrically stimulated. For example a blow to the face will often produce "flashes of light." This is because the shock actually makes the retina physically vibrate, which the brain interprets as flashes of light. In a young person of your son's age, the most likely cause of seeing flashes of light would be a migraine
. Migraine is a type of headache
in which blood flow in and around the brain is altered temporarily. This is usually felt as throbbing or pulsatile headache, but it is often proceeded by an "aura" which can include numerous symptoms such as nausea, dizziness--and flashes of light or wavy lines of light. Even if these flashes your son has are not subsequently followed by headache, it could still be migraine, because there is a variant of migraine called ocular migraine, which occurs just in the eye. The best step would be to have your son's eyes examined by his primary care or eye doctor
just to make sure that there is nothing more serious wrong, such as trauma to the eye. If this checks out, then it is probably migraine.