Mostly intensity is measured using photo diodes or photo resistors in the units of volts/ampere but I want to measure absorption of light intensity from a green led when it passes through my test sample with varying concentrations by using a Lux meter which gives intensity in LUX units. Can it make any difference in my measurement? Please I need your suggestions.....
Hello,
first a simple answer: No, you cannot just use a lux meter to determine intensity in W/m².
The problem is, you don't know the spectrum of the incoming light (...probably you know it from the datasheet) and what is also unknown is the spectrum after passing your experiment. Both is needed to calculate the conversion constant from measured Lumens to Watt. The 683lm/W holds true only for a V(lambda) emission spectrum, which is definitely not what you will get from your 530nm LED. I assume there will be a spectral dependence of your experiment, thus the conversion factor will differ from the one from your LED spectrum. If you know both factors and angular dependence stays unchanged w/wo experiment you can use a lux meter for measurement.
Dear,Mr Iftak Hussain
it has other technical for measuring light intensity,you use image of CCD without objective,and calculate the sum grayscale of this image.
Thanks sir, I know sir how to use ccd which we often did. But for my current work I have to use only lux meter.
Hi Iftak,
Your lux meter will measure the luminance of your LED in [lux] or [lm/m²]. You can easily convert it in [W/m²] ( 1W/m²=683lux @555 nm) or in [W] considering the size of your detector.
If you want to compare your measurements to those obtained with a photodiode, use the responsivity of your photodiode to convert your [Volt/Ampere] in [W].
Good luck.
Hello,
first a simple answer: No, you cannot just use a lux meter to determine intensity in W/m².
The problem is, you don't know the spectrum of the incoming light (...probably you know it from the datasheet) and what is also unknown is the spectrum after passing your experiment. Both is needed to calculate the conversion constant from measured Lumens to Watt. The 683lm/W holds true only for a V(lambda) emission spectrum, which is definitely not what you will get from your 530nm LED. I assume there will be a spectral dependence of your experiment, thus the conversion factor will differ from the one from your LED spectrum. If you know both factors and angular dependence stays unchanged w/wo experiment you can use a lux meter for measurement.
Hi Iftak,
If I understand your question correctly, all you want to do is measure optical absorbance of your sample? If that's the case the units provided by your lux meter (which after all is just a photodiode) are irrelevant as long as they are proportional to intensity. So, (with dark readings subtracted) T = Isam/Iref where Isam is the reading through the sample and I ref is through air or through a blank solution. Absorbance is just -log of that ratio. This will give an absorbance of the integrated band of light from the LED, which is probably on the order of 20 - 30nm FWHM. You can calibrate these readings to samples with known concentration of whatever you are trying to measure.
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