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Discussion Starter · #1 · (Edited)
I have two DIY PAR meters for sale. One, I made by converting a lux meter to read PAR by using filters over the photodiode, and sealing the complete, cut-down sensor in an acrylic case. Its readings are stable, and I have calibrated it against a 10,000K PC AHS light, a 6500K 23 watt screw-in CFL, and a 40 watt soft white incandescent bulb (just out of curiosity). The calibration is:

As you can see, it is very accurate for cool white fluorescent light, and previous calibrations have shown that with cool white LEDs the calibration is the same.

Here is what it looks like:

This calibration works only out in the open air, not under water. Under water, in a planted tank, the meter seems to read low, as much as 50% low, but I couldn't do an accurate calibration because it wasn't possible to find a well lighted spot at the substrate that was big enough to be expected to give the same reading for both this meter and a smaller sensor Quantum meter. It may be equally accurate in an otherwise empty water filled tank, but I can't demonstrate that.

I see the primary use for this meter to be measuring how much PAR you get from a light fixture propped across two chairs, just to characterize the PAR production of that light, to be sure you have an appropriate light for your tank. It is mounted on a clear acrylic strip, with a 3/8" diameter "socket" so a 3/8" dia acrylic rod can be used as a handle for using this in a water filled tank.

I will sell this for $50, with Priority Mail shipping included in the price. PM me if interested.

The second PAR meter is made from the indicator from a lux meter, with a DIY sensor, using an Excelitas VTB8441BH photodiode. This is a photo of it:

Its calibration is:

This one also has a 3/8" diameter "socket" so an acryiic rod or tube can be used as a handle for underwater use. This one, unlike the first one, has been tested underwater successfully. It has a very small aperture sensor, hoping this would eliminate any optical problems caused by the water, and it did just that. It is very accurate, reading about 4% too high when measuring PAR from "cool white" fluorescent or LED lights, but won't work with incandescent light due to the very different spectrum from that type of lighting. In natural daylight it is usable, but reads 20% too high, again due to the spectrum being different.

I will sell this one for $60, with Priority Mail postage included in the price.
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