light, photons, irradiance

[kadimkris]

So I'm not too sure what I'm doing here. I want to know how many photons there are in the given wavelength of "light". I have been digging for about two weeks in spare time. I am learning about plants and lighting and trying to make a project to build a light tailored to plants needs. At the moment I need to find out how to get total about of photons that are produced by a given light.

 

Terms I know "of":

mole (unit)

einstein ( unit)

Irradiance

"PAR"and "PUR"

plus some others

 

I have some background in electronics and engineering as this is what i am going to school for. just two days ago I learned the differences between optics for the human eye and measurements and true power are different . lumens, candle, etc vs photons etc. I am wanting to learn more about light and need steered in the right direction .

 

the issue at hand is that spec sheets have ton of info but most are geared towared the human eye can we take the info they give use and come up with irradiance in photons or einsteins. As i learn about botany (hobby) I have learned they have done test to show that this is the max amount of light a plant can use in this wavelength.

 

sorry for the long post and thanks for your time. here is a sample of a few lights i am looking at atm. note one is in unit lm and other mW.

 

 

cree xlam xr-c

 

spec sheet http://www.cree.com/...f/XLampXR-C.pdf

 

royal blue

wavelength range 450-465

min radiant flux 300 mW (+/- 7%)

350mA @ 3.6 volts dc ( this = .35*3.6= 1.225 watts )

 

red

wavelenght 620-630

luminous flux 39.8 lm (+/- 7%)

700 mA @ 2.4 volts dc ( this = .7*2.4= 1.68 watts )

Edited September 19, 2011 by kadimkris

[swansont]

If the light is monochromatic, it's just a matter of looking up the conversion on the graph of eye sensitivity. The maximum is 683 lm/Watt at 555 nm for photopic vision (which is probably assumed in the specs). The eye response graph shows that the luminous efficacy is about 0.4 of the maximum at 620 nm, or ~275 lm/W.

http://en.wikipedia.org/wiki/File:CIE_1931_Luminosity.png

 

That means about 150 mW. At 630 nm, the luminous efficacy is about 0.3 of maximum = 200 lm/W implying 200 mW. So somewhere in that range.