I am doing optogenetics on Drosophila larvae. I need to use the Blue light and I have to measure the light intensity. For this purpose, I am using "Sanwa Laser Power Meter LP1". The display shows the power of the light. However, I want to know is it the power of light per unit area? If it is, then what is the unit of the area?? mm2 or cm2 ?
Dear Reaz Uddin ,
please have just a look at the data sheet of your power meter (attached).
The display reading is according to the preset of the powermeter range in µW or mW.
The detector is a Si photodiode of 9mm in diameter.
So you can easily convert the displayed power into power per area.
However this conversion into power/area only makes sense when the spatial distribution of light is quite homogenous. Laser beams in general are quite smaller than 9mm. Thus in this case dividing the power by the detector area is nonsense.
But pay attention, that for your blue light you have to correct the displayed data according to the conversion table of spectral sensitivity characteristic and follow the instructions.
Good luck
Dear @Reaz Uddin,
Given the data sheet and probe design, this laser power meter is clearly designed to provide you with total laser power received at the detector, not power denisity. This will work as long as the projected light beam will not exceed the maximum area of the detector. Laser beams typically ar way smaller in diameter then 9mm. The meter is calibrated against a HeNe reference laser, which has a wavelength of 633nm. To measure the power of lasers at other wavelengths, you need to use the correction factors in the data sheet.
To get some more understanding of light measurements. look for The Light Measurement Handbook from Ales Ryer. This can be found on the web as a PDF. Very useful as a start.
Thank you Fokko Pieter Wieringa and Gerhard Martens for the reply. It was really helpful.
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