Actually, the chrome finish is the best. This is not my study, and I apologize to the person who did it, as I don't remember where I copied this post from so I can't give proper credit...
Start of post:
"Hey guys! I have been following this thread cuz i was kinda curious myself. So i borrowed a lux meter from a local LFS and did some experimenting. I couldnt get an exact reading on my main tank cuz i could not exactly dip the sensor of the meter in the water. I was getting some strange readings. I wanted to get a reading with the sensor pointing towards the light. So i experimented on my fuge instead. The water level in the fuge is low enough where i can get the sensor down in the fuge where it wouldnt get wet. The sensor was centered on the light about 10 inces down. Im not a light expert so i think the measurements are in lux. (whatever that means)
Open top
139900
White eggcrate thin side down
111800
White eggcrate thin side up
129500
Reflective eggcrate thin side down
149000
Reflective eggcrate thin side up
170300
So it looks like if you have to use eggcrates, thin side up! Oh, the light is one of those 65watt flourex from Home Depot. Hope this helps a little."