What's the difference/conversion factor?
Candlepower versus Watts
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Don Burke
Contributor
Candlepower is a measure of output and watts is a measure of input.
Since different bulb designs have different efficiencies, this would be tricky at best.
I'm also pretty sure you can change the candlepower rating of a light by changing the reflector.
An early question I would have is "what measure of output means the most to me?" Lumens or something like that may be more appropriate.
Since different bulb designs have different efficiencies, this would be tricky at best.
I'm also pretty sure you can change the candlepower rating of a light by changing the reflector.
An early question I would have is "what measure of output means the most to me?" Lumens or something like that may be more appropriate.
I just did a little research on this exact topic a few weeks ago. One of the guys I work with noticed that different lights are rated in different ways. Some are rated in candle power while others are rated in lumens. I found this little bit of info on the net...
Candlepower is a rating of light output at the source, using English measurements.
Foot-candles are a measurement of light at an illuminated object.
Lumens are a metric equivalent to foot-candles in that they are measured at an object you want to illuminate.
Divide the number of lumens you have produced, or are capable of producing, by 12.57 and you get the candlepower equivalent of that light source.
For more info on the topic click on this link and then on the "ASK" button at the top of the page.
Hope this helps,
Scott
Candlepower is a rating of light output at the source, using English measurements.
Foot-candles are a measurement of light at an illuminated object.
Lumens are a metric equivalent to foot-candles in that they are measured at an object you want to illuminate.
Divide the number of lumens you have produced, or are capable of producing, by 12.57 and you get the candlepower equivalent of that light source.
For more info on the topic click on this link and then on the "ASK" button at the top of the page.
Hope this helps,
Scott
donacheson
Contributor
It's not a simple factor. The first complication is that candle power and watts aren't the same thing expressed in different units. The second, and major complication, is that candle power (and the other variables of photometry) involve only energy that is visible to the human eye.
Watts and lumens are similar units, watts being a measure of radiant energy flux, lumens being a measure of only the visible part of radiant energy flux. Watts are also a measure of power (volts x amperes) input into an electric lamp.
I notice that physicists seem to avoid using the term "candlepower", but I'm taking the unit of candle power to be the candle and 1 candle is 1 lumen per sterradian. (A steradian is a measure of solid angle; for example, the size of a flashlight beam in two dimensions - up/down and left/right. There are 12.57 steradians in a sphere, and since 1 radian=57.3 degrees, there are
about 3283 square degrees per steradian.)
Thus, a flashlight which produces 10 lumens spread out over a 60 degree round beam is a 10 candle light, probably termed a 10 candlepower light by engineers. On the other hand, a flashlight which produces the same 10 lumens concentrated in a 6 degree beam is a 1000 candle light.
From what I read, ordinary small incandescent bulbs can produce about 8 or 10 lumens per watt of input power. Losses are heat and invisible infrared energy, so obviously watts and lumens are scaled very differently - in other words, a lossless source of light would produce many lumens (as many as 683?) for each watt of input.
Sales literature uses wattage to describe input power as was mentioned earlier. This of course only serves as a basis for comparing lights if everything else is equal. As commonly used "watts" tells us nothing about light output.
A radiospectrometer measures light in units of watts/steridian/meter^2 (raw data), which is essentially the power at each wavelength. That power spectrum can be converted to any other units that might be desired to describe color or intensity. Some units used are Lumens and Candellas for intensity and XYZ or LAB (there are other scales also) coordinates for color. There's more to it but that's the best I can do in a couple sentances and having been out of it for a while without reference in front of me.
A radiospectrometer measures light in units of watts/steridian/meter^2 (raw data), which is essentially the power at each wavelength. That power spectrum can be converted to any other units that might be desired to describe color or intensity. Some units used are Lumens and Candellas for intensity and XYZ or LAB (there are other scales also) coordinates for color. There's more to it but that's the best I can do in a couple sentances and having been out of it for a while without reference in front of me.
oxyhacker
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As I understand it, candlepower (usually really CBCP - center beam candle power) measures center beam brightness and lumens total light output which is really pertinent only if you mostly like to shine your light in people's eyes. Reflector bulbs get rated in candlepower and barebulbs in lumens, and there is no meaningful way to go from one to the other.
Watts are not much better. A 50w halogen bipins from the hardware store may produce 17 lumens per watt. A plain old non-halogen incandescent would be even worse - home lightbulbs are about 14. A halogen BRL bipin, which is identical to the hardware store version and interchangeable with it, will put out 28 lumens/watt! Of course the BRL is only good for 50 hours instead of, say, 2000.
An HID, on the other hand, will put out more like 64 lumens/watt. So that's a 4 to 1 spread in output for the same wattage, and we haven't even taken the extremes.
Watts are not much better. A 50w halogen bipins from the hardware store may produce 17 lumens per watt. A plain old non-halogen incandescent would be even worse - home lightbulbs are about 14. A halogen BRL bipin, which is identical to the hardware store version and interchangeable with it, will put out 28 lumens/watt! Of course the BRL is only good for 50 hours instead of, say, 2000.
An HID, on the other hand, will put out more like 64 lumens/watt. So that's a 4 to 1 spread in output for the same wattage, and we haven't even taken the extremes.
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