The Natural Philosopher wrote:
Ian Stirling wrote:

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.

No, fluorescents are about 15-25% efficient.
However there is nothing to beat them at the price yet. Most LED's are
pushing sub ten percent at best.

100lm/W is a typical sticker figure found for fluorescent lights.
This is 'white'.
As lumens is a unit of brightness, and at 550nm (green), it's 700lm/W.
But, for white light, it's lots less than this, as sensitivity in blue
and red is quite poor (but needed for colour rendition).

IIRC, it's around 300-200, depending on how close you want to get to sunlight,
so that'd put it at around 30-50%.
(the yellow street-light is nearly that efficient, but only does yellow.)