Lonewolfblue, this would have been better as a new topic.
To answer your question. It depends.
What putting something like reflective mylar in a fixture does is it will increase the amount of light reflected back down to the tank. If your light fixture is square, this will have little effect, if it has LOTS of smaller angles or is already kind of round or even better is triangle shape. It would help a lot more.
Before you spend the money on mylar, take some tinfoil and tape it into the light fixture. If you notice it's brighter, spend the money for the more permanent mylar, if not don't waste your money.
One Fish, Two Fish, Red Fish, Blue Fish