On Fri, 09 Dec 2005 15:03:06 -0500, Sawney Beane
wrote:
TKM wrote:
"Victor Roberts" wrote in message
...
On Mon, 05 Dec 2005 23:23:49 -0500, Sawney Beane
wrote:
Simon Waldman wrote:
Sawney Beane wrote:
There goes my theory. The next step is to increase my household
voltage so I can try out some British lamps. What voltge will I need?
Depends on how bright you want them to be :-)
European supply is nominally 230V nowadays. I believe that some US homes
have 220V available (am I right?), in which case this should light
British lamps quite happily, if not quite at full brightness.
FWIW, you will probably find things slightly dimmer for the same
wattage. One of the disadvantages of our higher mains voltage is that
incandescant lamps are a little less efficient.
I'll have to think about the math. If filaments were made of the
same wire, they would have to be four times longer in Europe for
the same wattage, but then they would run much cooler. I guess
European filaments are longer and thinner. How does that require a
less energy-efficient design?
Since we can always trade off life against efficacy we must
compare lamp efficacy for two designs at the same rated
life.
For the same wire diameter, a thinner wire must be operated
at lower temperature to achieve the same life. Lower
temperature leads to lower efficacy.
In America, standard 75 and 100W bulbs, which run about 750 hours,
are more efficient than 60 and 40W bulbs, which run about 1000
hours.
The higher efficacy comes from both the shorter life (750
hours vs. 1000 hours) and the fact that a 100-watt lamp can
use thicker wire then a 60-watt or 40-watt lamp with the
same rated life.
I once used a bridge rectifier and a capacitor to run a 15W
bulb at approximately 140 VDC. It was a pleasant light.
For flashlights (torches) 5v seems to work better than 2.5. I
think it's because the resistance at the various connections makes
less difference at the higher voltage. I wonder if there's an
ideal voltage for a flashlight.
You also need to consider end losses from the filament to
the support wire. Without end losses there would be no
"optimum" voltage for any lamp. The largest wire would
always be the best under these idealized conditions because
it could be operated at the highest efficacy. However, with
you balance end losses from the filament to the supports
against evaporation of the filament, you find an optimum
wire size and hence an optimum voltage for any power. The
optimum voltage is a function of power and rated life and
increases as the power increases.
--
Vic Roberts
http://www.RobertsResearchInc.com
One incandescent lamp optimization model that the GE lamp engineers used
some years ago kept pointing to 50 volts or so as the best for consumer
household lamps in the 40-150 watt range. The model took into account end
losses, filament supports, gas mixture wire diameter, lumen output required,
life, etc. as I recall.
Terry McGowan
I wonder how great the advantage is relative to 115 and 230. I
wonder if DC is better than AC. With modern semiconductors, would
it be worthwhile to build lamps to supply the ideal voltage for an
incandescent bulb of a certain wattage?
I don't have the data for an optimum voltage 100-watt lamp,
but you can see the effect by comparing 120-volt against
230-volt incandescent lamps. A typical 100-watt, 120-volt,
750-hour, frosted incandescent lamp has an efficacy of 17.1
lm/W while a 100-watt, 240-volt 1000-hour, frosted
incandescent lamp has an efficacy of 13.3 lm/W. (I can't
find 120-volt and 240-volt 100-watt lamps with the same
life.) Adjusting the efficacy of the 750-hour lamp for
1000-hour life reduces its efficacy to 16.4 lm/W, which is
still 23% better than the 240-volt lamp of the same life.
Also, I see a 100-watt, 34-volt 1000-hour frosted lamp
listed with an efficacy of 21.6 lm/W, while a 100-watt,
12-volt, 1000-hour frosted lamp is listed with an efficacy
of 17.5 lm/W.
One popular type of desk lamp uses an automotive brake bulb and a
12V transformer. Is 12V better than 50 for a bulb of 20W or so?
I'm not sure. Looking again at 1000-hour lamps, a 12-volt
25-watt lamp is slightly less efficient than a 34-volt
25-watt lamp with the same life. (I don't have data in 20
watt lamps.) Reducing the power reduces the optimum voltage,
but the efficacy at 50 volts may be above the peak for a
20-watt lamp.
--
Vic Roberts
http://www.RobertsResearchInc.com
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