You could paint the inside of the hood with the most reflective paint you can buy.
Locally, three options are available: A reflective white paint used for road signs, a 'chrome finish' spray paint, and a reflective self adhesive film made by 3M. I have used the 'chrome finish', since it was cheapest.
The difference in how much light goes into the tank is very noticeable.
If you put too much superglue, or the surfaces are not really smooth and level where they join, you will make a mess. A trick used by local aquarium repairmen for years is to hold the pieces of plastic together, sprinkle a line of sodium bicarbonate at the joint, and then apply the crazy glue. The bicarbonate will soak up the glue, and make a very strong bond.
That is how I made a little hood, but forgot to build a lid. Changing a bulb requires a contortionist and lots of vaseline.