I have used mirror inside the hood as reflector. Although i dont have any test result but it did not increase the light, it did not help much. Then i painted it white and saw noticeable difference. This was because mirror will reflect light but it needs to be aligned and shaped properly so that all the lights reflects inside the tank just like a car's or bike's head lamp, you need to make the reflectors geometry correct.
I would suggest painting it white if you cannot bend and give proper shape to the hood or relfector.