# Question converting Luminous Flux to Fluence



## Novus (Jul 1, 2014)

I want to achieve a 'fluence'/'power density' of about 50mW cm. I had a look at the data sheet for the XPE LEDs and the red LEDs have a luminous flux of about 50 lm at 350mA.


My question is: is there any way to convert luminous flux (lm) to fluence (mW cm(-2)?


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## AnAppleSnail (Jul 1, 2014)

Novus said:


> I want to achieve a 'fluence'/'power density' of about 50mW cm. I had a look at the data sheet for the XPE LEDs and the red LEDs have a luminous flux of about 50 lm at 350mA.
> 
> 
> My question is: is there any way to convert luminous flux (lm) to fluence (mW cm(-2)?



Going by this paper...


The Cree outputs at 650nm instead of 625 nM. Let's use 625 nM = 200 lumens per optical watt, because it's close. You should replace this value though.

sr = Steradian, a cone of a certain angle. That is, if you shine a flashlight forwards, the cone of light shines out just like this.

Good luck!


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## Dr.Jones (Jul 16, 2014)

Flux is about 100lm/W @ 650nm.
Luminous intensity for XP-E is about 16cd @ 50lm. 
Irradiance E is radiant intensity I divided by the squared distance d. 
So it's 16cd * 0.01W/lm / d^2 or 160mW / d^2,
e.g. 160mW / (20cm)^2 = 0.4 mW/cm^2 at 20cm distance.


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