View Full Version : Micro Watts per 5nm per Lumens ?

05/27/2008, 08:57 AM
Hi Sanjay

Ref article "Facts of Light Part1,Part2 and Part 3" we have seen several SPD Graphs for MH and Lamps where we have microwatts per 5nm per lumen on Y axis and wavelength in x axis, these are generally refered to as Relative Spectral Power Distribution Graphs. In such a graph obtained from Light manufacturers how do we calculate the number of photons available from the light source at that particular wavelength ?

or can we convert microwatts per nm per lumen into watts / meter square ?



05/27/2008, 09:03 AM
I don't see where you are getting the micirowatt per lumen from those graphs. Those are not relative spectral graphs they are absolute values measured at 18" from the lamp center. The units on the Y axis are spectral irradiance measured as Watts per m^2/nm at 2 nm intervals.

There is a direct conversion from energy to photons, and using that you can convert to photons at each wavelength, from the data in the graphs.


06/02/2008, 04:20 AM
Hi Sanjay,

I was referring to the Relative SPD Graphs from the Lamp Manufacturers and hence there they have microwatts per 5nm per lumen on the Y Axis against the wavelength on the X asix. Hence I had
my questions .....

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