Rating flashlights according to lumens.

eddieguy

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I have a fascination with flashlights that friends and family like to tease me about but they are just one of those things i just cant seem to have too many of.

I know there are some smart folks on this site because i been a member on here long enough to know so i thought id run this ? About flashlights by you all.

You see all the time on a flashlight that it has
A certain number of lumens so i wanted to know what exactly is a lumen and are there other factors that would determine how bright a flashlight really is.

The reason for my curiosity is that i have seen flashlights that seem to project a brighter light as opposed to one that advertised that they possessed many more lumens. Is there more at play here than how many lumens a flashlight supposedly has.
 

billr

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The short answer is that how the light is focused is of great importance. I'm not sure, but perhaps the light color is also important (the temperature in Kelvin degrees). I don't know right now if "lumen" ratings take into account what frequencies we can actually see.
 

nickb2

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“a unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.”
 

nickb2

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so, now, we must know, what is a (candela)

In french, I would assume that is latin for (chandelle) or candle in english.

nounPhysics
noun: candela; plural noun: candelas; symbol: cd

the SI unit of luminous intensity. One candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian.
 

nickb2

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then we have to understand what is a steradian

The steradian (symbolized sr) is the Standard International (SI) unit of solid angular measure. There are 4 pi, or approximately 12.5664, steradians in a complete sphere.

A steradian is defined as conical in shape, as shown in the illustration. Point P represents the center of the sphere. The solid (conical) angle q, representing one steradian, is such that the area A of the subtended portion of the sphere is equal to r2, where r is the radius of the sphere.
 

nickb2

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How many lumens are in a Kelvin?

google gave me this, and it sure makes sense



Light bulbs labeled as "warm white" all have CCTs of approximately 2,700 Kelvin. Specifically, a 40-watt 500-lumens incandescent light bulb has a CCT of 2,700-2,900 Kelvin; an 8-watt 450-lumens LED light bulb has a CCT of 2,700 Kelvin; and a 9-watt 450-lumens CFL light bulb has a CCT of 2,700 Kelvin.
 

nickb2

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what is a cct

Color temperature (Correlated Color Temperature, or CCT, in lighting tech jargon) is essentially a gauge of how yellow or blue the color of light emitted from a light bulb appears. It's measured in the Kelvin unit and is most commonly found between 2200 Kelvin degrees and 6500 Kelvin degrees.
 

nickb2

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The visible light spectrum is the section of the electromagnetic radiation spectrum that is visible to the human eye. Essentially, that equates to the colors the human eye can see. It ranges in wavelength from approximately 400 nanometers (4 x 10 -7 m, which is violet) to 700 nm (7 x 10-7 m, which is red).1 It is also known as the optical spectrum of light or the spectrum of white light.
 

nickb2

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Nanometer to HZ
Divide the wave's speed by its frequency, measured in Hertz. For example, if the wave oscillates at 800 THz, or 8 x 10^14 Hz, divide 225,563,910 by 8 x 10^14 to get 2.82 x 10^-7 meters.
 

nickb2

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I don't know right now if "lumen" ratings take into account what frequencies we can actually see.

See above.

If I am wrong, I will study further.
 

nickb2

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most ppl just want to know how many candles is this light worth.

Roughly, that is what a lumen is. But it is much more than that, and advertising confused that or the average joe such as us.

I some one says, this projector has 1000lumens, I say really, lets see.

Because 1000 candles dont have same wavelength as 1000 LED. Not same color spectrum, not same waveleangth, hence influences the kelvin, hence white burn hotter than yellow.

I guess, that is my un educated guess.
 
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