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.

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.

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.

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.

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