There are superb articles on incandescent and LE bulbs on wikipedia and howstuffworks.com (They can be a bit scientific/techie for some people I must admit)
http://en.wikipedia.org/wiki/Fluorescent_lamp
http://www.howstuffworks.com/light3.htm
http://science.howstuffworks.com/solar-cell.htm (thought I'd add this one for Jambuttys solar calculator problem)
Effectively what they are saying is that the number of lumens is teh same, its just the colour temp of teh light that changes. its this colour temp change that makes teh calc work 'better' with incandescent light.
Jambutty,
I do have one addition, you started talking about the RGB colour palatte, I think you should investigate the difference between the RGB(sRGB) and Adobe colour spaces for when you are talking about digitised colour as there is a significant difference in teh 'amount' of colours that can be described by each