Andrew Gabriel wrote:
In article ,
Ian Stirling writes:
Mark Wood wrote:
Probably a FAQ but here goes...

What is the relative HEAT output from one of these bulbs?
I'm presuming a '20W Energy use/100w Brightness' saver bulb puts out little
heat and is perfectly safe to use with a '60W Max' dangly paper lampshade.

But wanted to check... :+/

About 6-8W or so comes out of them as light, the remaining as heat.
Maybe half the heat comes from the ballast, and half from the tube.
The surface temperature of the tube is often around 100C.

Ballasts are quite efficient nowadays. Most heat comes from the tube,
where a number of laws of physics still contrive to severely limit the
efficiency.

Thinking about it, you're right.
Fluorescant tubes aren't too bad, even an ideal light source that took in
electricity and emitted white light, with no waste heat would only be about
twice as bright.
(the yellow street-light is nearly that efficient, but only does yellow.)