josephkk wrote:

On Mon, 30 Jul 2012 09:25:15 +0100, Martin Brown
wrote:

On 30/07/2012 03:25, Jim Thompson wrote:
On Mon, 30 Jul 2012 10:15:48 +1000, "David Eather"
wrote:

On Mon, 30 Jul 2012 09:53:26 +1000, Jim Thompson
wrote:

Loony Question for Today...

Which produces more HEAT, a 40W Incandescent, or a 40W Halogen bulb?

...Jim Thompson

Technically the incandescent. The both consume 40 watts but the halogen is
more efficient at converting power to light (and hence not to heat). I
said 'technically' because you are unlikely to notice the difference in
heat.

There are two forms of heat involved here. Thermal radiation and warm
air the relative proportions vary with the type of lamp.

You haven't defined what you mean by "heat" but taking it to be
thermally damaging radiation capable of scorching lampshades.

The *peak* emission even of the quartz halogen lamp is still in the near
infrared even for a halogen bulb run at 3300K so the flux of thermal IR
from a quartz halogen is more likely to start fires. The small red hot
envelope and tendency to explode adds to the excitement.

More short wave visible photons are emitted by the quartz halogen
filament at a higher temperature but well over half of them are high
temperature thermal IR (anything characteristic of 600K and above).

http://zeiss-campus.magnet.fsu.edu/a...enhalogen.html

Has graphs of the BB radiation curves for 2500K through 3300K.
This applet will let you plot some suitable curves as a function of
temperature set Tmax=3300 (tungsten isn't quite a black body)

http://www.phy.ntnu.edu.tw/ntnujava/...p?topic=1037.0

Mains quartz halogens come with a warning that they are unsuitable for
desk lamps in part for this reason (they are double glass envelope).

Once it has thermalised in the room 40W total dissipation is 40W of heat
ignoring any light that escapes out of the windows. You can feel the
beam of heat radiation from a directional quartz halogen fitting.

More light and heat radiation is emitted from a quartz halogen lamp as a
proportion of the electricity consumed and a higher percentage is at
visible wavelengths but the peak emission is still around 900nm.

An ordinary filament lamp loses a larger proportion of its heat by
convection of warm air from the physically larger but cooler glass envelope.

My thoughts, too. I have a fixture rated for three 40W miniature base
incandescents, presently loaded with three 40W Halogens. My
temptation is to go up to three 60W Halogens.

...Jim Thompson

Well if you want to set fire to the lampshades and burn your house down
go right ahead. I take it you flunked physics at MIT.

Geez. Did you do anything to validate the junk on those two sites?
Tungsten photofloods at 3200 k and 3400 k have been available for over 50
years. I can buy halogen lamps with operating temperatures as high as
5700 k, for my car even. Take a look at Plank's law for energy
distribution and Wein's law for spectral peak.

http://egglescliffe.org.uk/physics/a...ody/bbody.html

?-)

Tungsten melts at about 3700K, and boils at about 5800. Non-halogen
photofloods had very short lives--like 20 hours--and darkened very
significantly by about 10 hours. (I used them back in the 1970s when I
worked in a camera store.) Halogen ones last longer, because the high
gas pressure inside reduces filament evaporation.

I invite you to investigate the difference between colour temperature
and thermodynamic temperature. The emissivity of hot tungsten is
slightly lower in the IR than in the visible, so its colour temperature
is about 100K higher than its thermodynamic temperature, but the actual
filament doesn't get above 3300K.

Higher colour temperatures are obtained by using blue filters, i.e. by
absorbing a lot of the red and yellow. Not how you get

If there were any solid objects that could stand 5700K, incandescents
would win the luminous efficacy contest, and the greenies would have to
prop up their shaky self-worth by disapproving of us for something else.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net