"Jeff Liebermann" wrote in message
news
On Fri, 4 Jul 2008 01:23:49 +0100, "Arfa Daily"
wrote:
I have noticed that these new smaller bulbs run a whole quantum leap
hotter
than the older larger size, and they hot up the shade on the bench light
until it is unbearably hot to touch.
As I understand it (possibly wrong), the higher the temperature of the
filament, the more efficient the incandescent light bulb in lumens per
watt. There's a bit of a clue at:
http://en.wikipedia.org/wiki/Incandescent_light_bulb
During ordinary operation, the tungsten of the filament evaporates;
hotter, more-efficient filaments evaporate faster. Because of this,
the lifetime of a filament lamp is a trade-off between efficiency
and longevity. The trade-off is typically set to provide a lifetime
of several hundred to 2000 hours for lamps used for general
illumination. Theatrical, photographic, and projection lamps may
have a useful life of only a few hours, trading life expectancy
for high output in a compact form. Long-life general service lamps
have lower efficiency but are used where the cost of changing the
lamp is high compared to the value of energy used.
In other words, the newer smaller bulbs are trading efficiency for
lifetime, which is the result of running hotter. I'm not sure why the
bulb is smaller. My guess(tm) is that it's simply thicker, which
allows the use of a smaller bulb size, which can withstand the heat
better than a thin bulb and can handle a higher internal gas pressure
(which is necessary to prevent filament evaporation).
More on the subject:
http://en.wikipedia.org/wiki/Luminous_efficacy
http://members.aol.com/ajaynejr/lumen.htm
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Interesting thoughts. Really not a good thing though, I am thinking. It's
only been a matter of a few months that I have been using these small bulbs,
and they have already caused a problem with a lamp that had previously been
running daily, without heat-related problems, for years. It seems to me that
in certain domestic applications, these could represent a significant fire
hazard. Take for instance, a 'standard' pendant room light fixture,
suspended on normal plastic cable. There is not normally enough heat
generated, to cause a problem with the insulation, but I'm sure that with
the increased temperature that these things run at, there's going to be.
Take also, a typical lampshade made from either plastic or paper based
sheet. These will typically have a sticker in them saying something like "60
watt max lamp". Now that figure is a fire safety one, based on the heat
generated by a typical 60 watt bulb. What about when you put one of these
new ones in ? I would guess that the heat steaming off them, is at least
equivalent to what you would be expecting from a traditional-sized 100 watt
bulb. So even putting in a correctly rated 60 watt bulb, you could be
thermally overloading that shade, by 60 odd % . Potential fire hazard, or am
I just being paranoid ? Does this need bringing to someone's attention ?
Arfa