|WikiProject Measurement||(Rated C-class, Mid-importance)|
Calibration of lamps
I doubt that there is a direct relation between the cp value and lm value of a light source? Because there is no direct relation between the cd and lm. And the cp value is a factor of the cd value. But using cd (or cp) for the description of a source is not adequate. The cd that light source emits depend on the angle of the measure. If you measure perpendicular to the filament, then the value will be higher than measured from the side. So my question is: what use does the cp value have? I know it's an obsolete unit. But it is still used: http://www.pmlights.com/bulbs.cfm --TeakHoken220.127.116.11 (talk) 12:03, 5 November 2008 (UTC)
I found the answer: http://www.donsbulbs.com/cgi-bin/r/d.pl/cp.html ; http://www.donsbulbs.com/cgi-bin/r/d.pl/mean_spherical_candlepower.html . Seems that MSCP can be converted into lm.--TeakHoken18.104.22.168 (talk) 14:49, 5 November 2008 (UTC)
Should we have a section on measuring candlepower, since it is, after all, within the scope of WikiProject Measurement...?
Anyway, I'm no math whiz, but from what I can tell, the following procedure could be used to verify the candlepower output of a flashlight. (Many consumer flashlights are rated in candlepower, but what consumer can test them?)
Since 1 candlepower is one lumen per steradian, and a steradian is equal to the radius of a sphere squared, and a lumen is the total quantity of light ("photons per second") emitted by a standard candle in one steradian, then we know that if we put a piece of paper 1 foot from a candle, it will be illuminated with 1 lumen per square foot. So this will be our reference.
So let's say our flashlight is rated at 1000,000 candlepower -- we take the square root of that (which is 1000) and we place the flashlight 1000 feet away from our candle.
We then set up a light shield so that the candle (from 1 foot away) shines on one half of a piece of paper, and the light from the flashlight (1000 feet away) shines on the other half --- then we can see which is brighter. They should be equal, if the flashlight is really 1,000,000 candlepower.
You see, at 1000 foot, the area (in square feet) of one steradian will be a million square feet. Thus, the one square foot will be one millionth of a steradian, so if the paper target is illuminated with one lumen per square foot, (which we compare to the candle that also delivers one lumen per square foot at one foot), we then see that the flashlight delivers 1 lumen over one square foot -- which is one millionth of a steradian -- so, since candlepower=lumens/steradians, we divide the 1 lumen by the millionth of a steradian and get 1000000 for the candlepower rating..
Candle image relevance
Is the picture without caption relevant to this article, or should it be removed? The information I get from the picture is just: "this is what a candle looks like". — Preceding unsigned comment added by SuperSpaceAdventure (talk • contribs) 06:58, 12 October 2012 (UTC)
- It implies to me that a candle such as the one in the image is a 1 candlepower source, which is approximately true. 12:10, 12 October 2012 (UTC)