Ya look for a leak. if you cant spot one right away, fill the res and use a rod or stick to push the pedal down and then go look for a leak. Not in your case but sometimes when the light comes on it means you need new brake pads because the pistons of the caliber now are sticking out a lot do to the pads being worn down. So if you full the res and then put new pads on it over flows the res. Cuz you push the pistons back into the caliper.
