Thursday, August 12, 2010

CFL Spectrum with Gamma Correction

The vertical scale of the intensity for the CFL spectrum found in the last blog is nonlinear due to the fact that the camera uses gamma compression to raise the values at the bottom of the scale making the image more sensitive to lower light levels. The images have to be gamma corrected by the display device. The value of gamma that was agreed upon for sRGB is 2.2.

The plot above is for the same CFL spectrum found previously but with a gamma correction applied to the vertical scale. The relative heights of the peaks are probably dependent on the formula for converting the RGB values to a B&W value. The function that my computer uses to convert a color image to B&W shows a stronger response to the G values which one would expect since the eye is most sensitive to 555 nm. I probably need to look for a better conversion formula.

edit: The eye's response to light of different wavelengths is measured by the luminosity function. The RGB values are determined by the color matching functions. All four depend on the illuminant since the spectral power density is a function of wavelength. The conversion formula used may assume a standard illuminant.


IN said...

Ok so I was reading up on the luminosity function and how meters calculate LUX and luminosity flux. From the little I have read it seems like a worthless measurement for any application that does not relate to how sensitive humans are to certain wave lengths. However they put a lot of stock in those measurement at the algae lab I work at for measuring efficiency of lighting. I tested an LED grow light and according to the LUX it is not as efficient as you would think an LED would be, but I think this is because it has no green spectrum. It only has ~450nm and 630-700nm according to my spectrometer. (EPP2000-HR) To me that seems more efficient for photosynthesis, and that is how it is advertised. Do you know of a way to quantify this efficiency compared to CFLs or HPS that doesn't use the luminosity curve? Maybe I am way off on my reasoning which is a good possibility as I have little experience with spectroscopy outside of what little they cover in gen phy and orgo. Could you offer me some insight into the subject?

IN said...

Also what was the color temp of the cfl you used?