Luminous flux caluclation from Ocean Optics Spectral data

[Radman]

Hello all,

Has anybody written a vi for calculating luminous flux based from spectral data obtained from Ocean Optics spectrometers?  I have written a VI but my answers keep coming up short when comparing it to a calibration lamp.  Here is my procedure for making the calculation:

1) Use LS-1 calibrated light source to calibrate the spectrometer+fiber. This generates a file that has units of uJ/count.  Multiply by 1E-6 to convert it to J/count.

2) Collect spectrum of source and subtract dark frame (no light).

3) Convert file generated in 1) to W/(sec*count) by dividing calibration file by the integration time used to collect spectrum in 2).

4) Multiply the the converted calibration file by the background corrected source file.

5) Isolate data in 4) from 380-830 nm. Use cublic spline function on background corrected data to generate dataset with the same wavelength as the 1924 luminious effacy function.

6) Multiply data in 5) by the 1924 luminious effacy function (V(lambda)). Make sure that the wavelength match for both datasets.

7) Integrated data and multiply by 683 (converts W to lm).

I have check my code several time and I keep getting answers that are roughly 40% less...

Thoughts?

Thanks,

Jay C. Poret, Ph.D.

SAIC

[AnalogKid2DigitalMan]

In step 7) the factor of 683 lumens/watt is based on light adapted sensitivity of the eye at 555nm. The value changes for different wavelengths.

For dark adapted sensitivity the value of 1700 lumens/watt at 507nm is used.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html#c2

Oddly enough 683/1700 = .4017 which matches your 40% less than expected results.

Just a wild guess on my part out of a pure coincidence.

[Radman]

That is a good observation but what I am looking to calcuate is the photopic response, not the scotopic response.  I will relook at the Ocean Optics Spectrasuite and see what values they are reporting.  I am pretty sure that they report the photopic value.  I cannot for the life of me figure out what I am doing wrong.  I will post my VI tomorrow...

Jay 

[Nasos]

Hello,

The calibrated spectrum that you get from your vi is identical to the SpectraSuite calibrated spectrum (Absolute irradiadiance graph in uWattt/cm^2/nm) when you are use the same calibration file? OR Is it aprox 40% lower from the SpectraSuite one?

Nasos