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| Cheapest way to check if a UVC bulb is as advertised? |
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| LaserSteve:
For measuring lasers above about 15-20 mW, we use what is basically a Absorber mounted on a Pelter element in reverse, which is the core of many laser power meters. While it is possible for a Hobbyist to build one, the issue is that they respond to pretty much "EVERYTHING" around them. Which is why my post above stresses finding the wavelength. Carbon black in the form of Black Krylon Engine Paint is generally a good start for the absorber, with a decent instrumentation amp circuit on the Peltier. Calibration, however, is an art form, with the classic means being a heater coil. You need a massive heat sink on the other side of the array. UV low pass glass filters or dichroric filters don't grow on trees, making this task a bit difficult. Fluorescence conversion can be anything but linear unless you have in-organic phosphors. SO: If you've got 100$ to spend you can get a GaP photodiode from Thorlabs. If you go GaP, I hope you can find a decent Ampere per Watt curve for a representative device. Part number is FGAP71 Photonics is easy, but accurate quantitative photonics is difficult and expensive. Steve |
| Zero999:
--- Quote from: LaserSteve on April 04, 2020, 10:29:55 am ---UV low pass glass filters or dichroric filters don't grow on trees, making this task a bit difficult. --- End quote --- I would have thought you'd want high pass, not low pass filters, unless your source has considerable energy above the useful germicidal frequencies, although it would produce a lot of ozone, if that were the case. I think lots of those cheap UV lamps will really be black light and there will still be a significant thermal IR blackbody, which would both be picked up by a bolometer. Cooling would reduce the blackbody emission, but it will affect the efficiency of the lamp. |
| LaserSteve:
I have attached an optical "Shortpass" typical graph from the Edmund Optics website. Optics uses the terminology just a little differently: |
| pipe2null:
What do you think of these photodiodes? $30-ish on digikey with reduced responsive range, no filter required for UVC/germicidal detection range but only "0.076 mm2" active area: https://media.digikey.com/pdf/Data%20Sheets/Photonic%20Detetectors%20Inc%20PDFs/SD008-2171-112.pdf $350-ish on digikey, has "1 cm2" active area but has normal response to visible light, requires filter etc.: https://optodiode.com/pdf/UVG100.pdf |
| Zero999:
--- Quote from: pipe2null on April 04, 2020, 07:22:46 pm ---What do you think of these photodiodes? $30-ish on digikey with reduced responsive range, no filter required for UVC/germicidal detection range but only "0.076 mm2" active area: https://media.digikey.com/pdf/Data%20Sheets/Photonic%20Detetectors%20Inc%20PDFs/SD008-2171-112.pdf $350-ish on digikey, has "1 cm2" active area but has normal response to visible light, requires filter etc.: https://optodiode.com/pdf/UVG100.pdf --- End quote --- The big sensor has a greater response in the near IR, than UV, so it would be a challenge to filter. The current from the small UV-only sensor is tiny, but the data sheet specifies it with a 306nm source, which it has little sensitivity to: only 68fA at 10mW/cm². Going by the response graph, it should be 25 to 30 times more sensitive to germicidal wavelengths, but it still isn't very much. It will be fun designing a circuit to work at such low currents, an ultra low bias current op-amp is a must a lens or parabolic mirror could be used to provide more gain, but the former might be expensive/difficult to get hold of and the reflectivity of some metals might not be as good at such short wavelengths, making the latter difficult to do. |
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