[PW] measuring the brightness of artificial lights

[Early, Charles T. (GSFC-272.0)[LIBRY]]

And wattage is a measure of how much electrical power a light consumes,
not how much light it produces.  Fluorescent lights are more efficient
than incandescendent bulbs, so a 20 watt fluorescent may produce as much
light as a 75 watt bulb. 

These different ways of measuring brightness measure different things,
so it's difficult to compare them.


Charles Early                              
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Goddard Space Flight Center               Charles.T.Early at nasa.gov

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-----Original Message-----
From: project-wombat-open-bounces at lists.project-wombat.org
[mailto:project-wombat-open-bounces at lists.project-wombat.org] On Behalf
Of BETZ-ZALL, JONATHAN
Sent: Wednesday, April 30, 2008 3:17 PM
To: list at project-wombat.org
Subject: Re: [PW] measuring the brightness of artificial lights

There is also the lux, defined in Britannica:

unit of illumination (see luminous intensity) in the International
System of Units (SI). One lux (Latin for "light") is the amount of
illumination provided when one lumen is evenly distributed over an area
of one square metre. This is also equivalent to the illumination that
would exist on a surface all points of which are one metre from a point
source of one international candle (candela). One lux is equal to 0.0929
foot-candle.

Cheerio!  Jonathan

-----Original Message-----
From: project-wombat-bounces at lists.project-wombat.org
[mailto:project-wombat-bounces at lists.project-wombat.org] On Behalf Of
BETZ-ZALL, JONATHAN
Sent: Wednesday, April 30, 2008 12:16 PM
To: list at project-wombat.org
Subject: Re: [PW] measuring the brightness of artificial lights

Here's an article from Britannica online:
http://www.britannica.com/eb/article-9049341/luminous-intensity
Note the relationship between the lumen and the candela.
Here is the article on the candela, which seems to have replaced
candlepower: http://www.britannica.com/eb/article-9019949/candela

Cheerio!  Jonathan Betz-Zall, Highline Community College, Des Moines, WA

-----Original Message-----
From: project-wombat-bounces at lists.project-wombat.org
[mailto:project-wombat-bounces at lists.project-wombat.org] On Behalf Of
Solomons1pal at aol.com
Sent: Wednesday, April 30, 2008 12:06 PM
To: list at project-wombat.org
Subject: [PW] measuring the brightness of artificial lights

Colleagues,
 
   While shopping for a really bright flashlight or lantern, I've  noted
that manufacturers and dealers have no uniform way of indicating how
bright their products are.  I've seen brightness described in at least
four  ways:
lumens,
candlepower, wattage, and foot-candles.  Is there any way of  converting

these metrics into one standard one, so that a buyer can compare  apples
with apples?
 
                                    Mark  Halpern



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