DIYbanter - Slightly OT. Heat and a Bench Light ...

"Jeff Liebermann" wrote in message
...
On Mon, 7 Jul 2008 09:53:39 +0100, "Arfa Daily"
wrote:

The things I do for science !!

Cease complaining. It's your question that I'm trying to answer.
Never mind that I don't know anything about light bulbs.

I have
two other types from the same stable, and one of the boxes has an energy
rating on it, and one doesn't, so I'll have to look next time I am in the
store.

Methinks there will be a difference in efficiency rating. If true,
that implies that the newer smaller bulb is really a Halogen filled
bulb, even though it's not marked as such.

OK. On the diameters. Consider them for all practical purposes, to be a
sphere. The old was 60mm almost exactly, and the new, 50mm almost exactly,
measured with an electronic calliper, so reasonably accurate figures.

Surface area of a sphere is 4Pi*r^2
Old = 4 * 3.14 * 3.0^2 = 113.0 sq cm
New = 4 * 3.14 * 2.5^2 = 78.5 sq cm
The new bulb has about 70% of the surface area as the old bulb.
However, I gotta dust off the college thermodyamics texts before I can
figure out the expected temperature rise given identical power
dissipations. I also gotta lookup the IR transmissivity of glass. The
things I do for science...

--
Jeff Liebermann

I was in the store today, and had a look at the boxes these bulbs are in.
There is no mention at all of them being a halogen type, but all of the ones
that are genuinely halogens, do say so. The energy rating on the box was "E"

Arfa