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Re: luminous efficiency (was Re: Season misconceptions in newspaper)



"Carl E. Mungan" 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.)

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***
---------------------------------------------------------------------
40 w (I) 490 lm 12.3 lm/w 0.72 w 1.8 % 98.2%
---------------------------------------------------------------------
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 %
---------------------------------------------------------------------
175 w (Hg) 7900 lm 45.1 lm/w 11.6 w 6.6 % 93.4 %
---------------------------------------------------------------------
125 w (Hg) 6000 lm 48.0 lm/w 8.8 w 7.0 % 93.0 %
---------------------------------------------------------------------
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 %
---------------------------------------------------------------------
70 w (Na) 6300 lm 90.0 lm/w 9.2 w 13.2 % 86.8 %
---------------------------------------------------------------------
150 w (Na) 16000 lm 107 lm/w 23.4 w 15.6 % 84.4 %
---------------------------------------------------------------------
* note: (I)=incandescent, (F)=fluorescent,
(Hg)=mercury vapor, (Na)=high pressure sodium
** 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>.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright Retired Physics Teacher
<exit60@cablespeed.com> Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Good judgment comes from experience,
and a lot of that comes from bad judgment.
- If you're leadin' the herd, take a look back
now and then to make sure it's still there.
- A good time to keep your mouth shut is when
you're in deep water.
- If you're lookin' for permanent employment,
scratch a dog.
- Learn from the mistakes of others. You ain't gonna live
long enough to make 'em all yourself.
-- from The Cowboys' Guide To Life
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~