is the bulb bad? try replacing the bulb.
if not, here is a 'po man's way of creating more reflection from the bulb...(I am cringing at the backlash I may get from this...but...)I take aluminum foil and make a large "reflector" background behind my bulbs in the tank top on my 25 gallon tank that doesn't really have any plants to speak of...the ones I have are floating banana plants that I put in there for my african butterfly to "hide" in. and they flourish! This certainly isnt a solution if you are looking to grow high wattage plants, but if you are just looking for a little boost to the light you currently have, this has worked well for me! Just brightens things up a bit. and it's outta sight, if you are careful about the placement of the foil then the only time you see it is when you lift your hood up.