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Re: luminous efficiency



Larry Cartwright commented on what I wrote:

> Hence luminous efficiency = lm/W - typically 17 lm/W for incandescents and
100 lm/W for fluorescents - these are the benchmarks you want to compare
your bulb to for claims of efficiency.

I'm not sure what you mean by "typically" and where you got your
numbers; but according to information I collected (right off the
packaging), there is a lot of variability in the efficiency of lamps by
size, with a marked efficiency increase as power input increases. I
published the following table to the PhyShare list back in December
1999. A quick look today at The Mart indicates that not much appears to
have changed since then. (There are no halogen lamps represented in the
data.)

Thanks, great table. For incandescents I meant the average of 60-150
W bulbs typically used. I agree that higher wattage means higher
filament temperature, which tends to increase the light output in the
visible by Wien's law.

For fluorescents it does look like 100 lm/W is an overestimate (65
lm/W looks like a better average value from your table), but I was
quoting that value from what I heard at CLEO a few weeks ago, as a
minimum goal for LED lighting to become competitive. (100 lm/W is not
hard for a single-color LED, but quite a bit harder for true white
lighting because of downconversion losses, which is also a loss for
fluorescents of course.)


TABLE: COMMONLY AVAILABLE ELECTRIC LIGHTING "BULBS"
(listed in order of increasing efficiency)

Electrical Visible Output/ Visible Efficiency: Loss:
Power Light Input Light Light Output
Input,* Output, Ratio Power Power Out/ Other
Watts Lumens Output, Electrical Than
Watts** Power In Light***
---------------------------------------------------------------------
60 w (I) 865 lm 14.4 lm/w 1.3 w 2.1 % 97.9 %
---------------------------------------------------------------------
100 w (I) 1710 lm 17.1 lm/w 2.5 w 2.5 % 97.5 %
---------------------------------------------------------------------
150 w (I) 2780 lm 18.5 lm/w 4.1 w 2.7 % 97.3 %
---------------------------------------------------------------------
15 w (F) 900 lm 60.0 lm/w 1.3 w 8.8 % 91.2 %
---------------------------------------------------------------------
28 w (F) 1750 lm 62.5 lm/w 2.6 w 9.2 % 90.8 %
---------------------------------------------------------------------
39 w (F) 2780 lm 71.2 lm/w 4.1 w 10.4 % 89.6 %
---------------------------------------------------------------------
* note: (I)=incandescent, (F)=fluorescent
** note: 683 lm = 1.00 w-equivalent (by candela unit definition),
i.e. a "perfect" 1-watt lamp would produce 683 lm of light.
*** note: Output "other than light" is mainly thermal and IR energy.

The complete posting is in the list archives at
<http://lists.psu.edu/cgi-bin/wa?A2=ind9912&L=physhare&P=R1707>.

--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/