Cover the reflector with mylar. Cheap, easy, and much more reflective than the original design.

You could also use metal tape on top of the tubes to shunt all of light downwards; or spray the inside reflector with silver metallic colored paint...

Paint the reflector flat white.

Remember, white reflects all visible colors. Metal and mylar reflectors only reflect what's been reflected off of a surface to begin with.

"Remember, white reflects all visible colors. Metal and mylar reflectors only reflect what's been reflected off of a surface to begin with."

That's not true. Light doesn't keep a "history". The difference between a mirrored surface and a white surface is that white scatters light while mirrored surfaces directly reflect the light. Scattering is better for plants, mind you, but not for the reason that you described.

"That's not true. Light doesn't keep a "history". The difference between a mirrored surface and a white surface is that white scatters light while mirrored surfaces directly reflect the light."

You're correct, I wasn't thinking straight, too distracted by gaming when I responded. XD

As for using foil tape on the back of the bulbs, I don't recommend this. If you're pushing that light back through the glass three times effectively. Once as it goes thru the glass to hit the reflective layer, again as it passes through, and then a final time at the other side of the bulb. You'll get a brighter spot but you're cutting down on actual emitted light as glass itself acts as a filter.

The glass isn't going to be filtering that much light. Besides, it's not like you're putting a mirror image there, it's going to scatter a little bit and a white reflector is going to push just as much light through the glass anyway.

Whether it's scattered or not, the bulb is the same size and casts the same "shadow" from the perspective of the reflector. Whether the light is traveling focused or scattered, the bulb is in the way of the same amount of light.

Somewhere I recall reading (I can't find a link now.) that titanium dioxide was a better white for reflectors than some other whites. The context was with regard to reflecting surfaces in museums, not for plant lights, so this tidbit may not mean anything here.

Many decades ago some light bulbs were sold with a silver metallic reflector in or upon the bulb. Someone apparently once thought that this was useful for some reason.

There is a lot of information at full-spectrum light sources. It is not too difficult for one who has a modicum of science education. It has some nice graphics if you like that sort of thing.

Titanium dioxide is an excellent and cheap scatterer of visible light. It's used in sunscreens for that reason. Also -- little known fact about titanium dioxide -- when exposed to UV and moisture at the same time, it encourages the formation of free radicals and thus helps sterilize itself. The smaller the particles, the more significant this effect.

I'd advise using white paint (which pretty universally uses titanium dioxide to make it white) on the walls of your growing area, and mylar on the reflector. Mylar works good on walls and such too, but the cost can be a concern, as well as the potential modification of the room (holes in the walls etc) that can worry renters.

The nice thing about the white paint is that it never goes out of style, too.