can someone explain to me the science of why light tube manufacturers only use one reflective tube per dome? Would there be that much of a loss of light to have it split into two tubes? Anyone having problems with these systems?

I would think it is to make it simple to install and cheap. If you do want to split it up you would cut the light to whatever each tube size was.

I would like the benefit of multiple light "fixtures" without having to install a dozen of those domes in my roof. A salesman at a trade show said that the light would be "weakened" if it was split up. Sounds like they want you to buy multiple complete units for multiple light "fixtures".

Say you have a 2 foot by 2 foot square. If all that light passed down you would get 4 square feet of light. Now if you take that same opening and divide it in to four 1 foot by 1 foot each one will have the output of 1/4 of what a single 2 foot by 2 foot would. Just by adding more "outlets" you don't get more light out, it just divides it.

But I am with you that I would rather have a single larger "hole" in the roof that in turn lead to multiple locations.

Having said that I am not a huge fan of skylights in general as I believe you lose more energy out than you gain in light energy, at least up north where I live. Then again there is that natural light factor that comes in to play.

check out sun tek manufacturing  http://www.sun-tek.com/

they have a multi unit.  I have never seen one but they are out there.

Cheers,
Eric

You might also look at a heliostat - it will beam a lot of light deep into a house.

http://www.practicalsolar.com/applications.html