The plants should grow toward all the reflective surfaces but not sure if gravity has something to do with it. I use mylar on 3 sides of my terrariums with white gravel in the bottom so there's light coming from all directions except the front. I could see a major heat build up if not vented. Am I missing something?

The most important ramification is that, in a perfectly reflective environment, the PAR watt rating of lamps would be meaningless because wavelengths that are normally reflected by plants will be absorbed and therefore show greater photosynthetic activity than otherwise predicted. For example, green fluorescent tubes would perform better than predicted by their PAR watt rating and, maybe, for all I know, perform better than tubes with mostly red and blue output.

Since a completely reflective environment doesn't exist, I developed a simplified model to help predict light absorption by plants under a canopy of fluorescent lights here:

http://groups.google.com/group/sci.physics/browse_thread/thread/0eac3e316ed06c45#

Just a little over my head but I get the idea. Now suppose the reflected surfaces were cylindrical in shape or the light was placed in a reflective pipe. Would the same figures apply?

Now suppose the reflected surfaces were cylindrical in shape or the light was placed in a reflective pipe. Would the same figures apply?

No, except in the ideal case of perfect reflection. White acrylic paint is around 80% reflective. If the light bounces just twice between painted walls before hitting a plant, 1 - 0.8*0.8 = 36% of the light will be absorbed by the walls.

Apparently, barium sulfate powder with a very small amount of binder is much better than white paint, but you wouldn't want it dropping on plants or soil. I suspect that it might be feasible to use barium sulfate with a very small amount of binder on vertical walls where any loose powder would drop away from plants, but, then you would have to careful to avoid strong air currents in ventilation.

See http://www.usu.edu/cpl/PDF/Barium_Sulfate.pdf

There are rumors that the reflectivity of aluminized mylar is 98% but I can only find reliable sources of information that say it is around 80%. See Excerpt

I can definitely see a difference between aluminum foil and mylar. My plants are receiving more light since changing to mylar. I have never hung it in the front of the terrarium though. I will try it to see if there's any noticeable difference in plant growth. It never hurts to try. Thanks for the science lesson .....John

Why would plants absorb wavelengths of light that they normally reflect? I don't think that's possible.

Why would plants absorb wavelengths of light that they normally reflect? I don't think that's possible.

In a perfectly reflective chamber, the light bounces back and forth between the plants and the walls until all the light is absorbed by the plants. A perfectly reflective chamber is impossible but I suspect that it is possible to increase a plant's absorbtion of, for example, green light to more than 80% by using a very reflective material such as barium sulfate on the walls.