As far as I know, 明かり is an artificial light source like a lamp, ceiling light while pertains more to natural light 光. For example. 太陽の光 instead of 太陽の明かり 明かりをつけて下さい。When said without context would most likely translate to a room light as opposed to turning on sunlight or any other natural source. "Hikari" example: 光が世にやって来た。