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Re: Season misconceptions in newspaper

Bernard is right on the mark regarding "luminous efficiency", but that may or
may not be what "efficiency" on a light bulb's package means. Labeling laws
and regulations (federal or state) may or may not rule on the use of
"efficiency" for light bulbs; it may be a term distinct from "luminous
efficiency" and in fact it may be legally undefined.

I'm not too keen on the lumen, myself. The V(lambda) curve that the
realization of the lumen at frequencies other than 540 THz (~555 nm in air)
is based on was derived using an extremely small population of study
participants, is heavily biased (e.g., they were all males, as I recall, and
we know that women's photopic response can differ), and is generally
considered to have been done by rather crude means (by today's standards).
Yet, it's the best thing that ISO/CIE has been able to find consensus on.
Even later curves have been derived but the original one is still the
consensus standard.

This has been a topic of conversation between Barry Taylor (NIST) and me a few
times, since Barry was serving as our country's representative on the
Consultative Committee on Units (CCU) for the CIPM when we spoke. Apparently,
in addition to the CIE being unable to come to a better consensus (and
recommending it to the CIPM) for a visual response curve the battle between
photometric and radiometric fans is akin to the old range wars between sheep
herders and cattlemen.

source: Parr, Albert C., 2001: The Candela and Photometric and Radiometric
Measurements. Journal of Research of the National Institute of Standards and
Technology, January-February 2001. [J. Res. Natl. Inst. Stand. Technol. 106,
151 (2000)]

On Monday, 2004 February 02 12:03, Bernard Cleyet wrote:
In reviewing mail for deletion I read the below and think JC's question
was not answered (I read the thread, but not carefully.)

"Perhaps they put out more light in the more visible portion of the
spectrum to validate the claim of higher efficiency?"

Many optics books (especially if written for engineers) begin with
concepts in radiometry and photometry -- defining their corresponding
units, etc. the difference is visual. photometry refers to light (that
portion of the EM spectrum the std. observer "sees") while radiometry is
limited to the region defined under discussion. e.g. the total
radiation from a given source. Therefore, since the lumen is a
photometric unit, luminous efficiency already takes into account the
energy in the visible and its stimulus of the std. observer.


John Clement wrote:
That may be true, but the tag actually implied you were saving
electricity. It did not have any information about lifetime or bulb
cost. It looked so impressive until you read the actual information.

What surprised me is that 60W halogen bulbs have comparable rated light
output to 60W regular bulbs the last time I looked at them in the store.
They usually have some claims about being "more efficient". Perhaps
they put out more light in the more visible portion of the spectrum to
validate the claim of higher efficiency?

Things have not changed since they sold in radio ads genuine 14 carat
simulated gold rings.

John M. Clement
Houston, TX

-----Original Message-----
From: Forum for Physics Educators [] On


Of Tim Folkerts
Sent: Saturday, June 21, 2003 3:32 PM
Subject: Re: Season misconceptions in newspaper



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