I remember Apogee stating that you should use the sunlight calibration for metal halides. I'm pretty sure that they said to use it for LEDs as well. Also, it's not a straight 10% difference, the response curves are different.
Apogee Instruments Quantum Sensor - PPF Under Different Light
CJ
well its 10% sunlight to CWF and 2% or 8% to MH. So it really doesn't matter which one you use for MH....Electric calibration is less than 2% low and sunlight is 8% high....so electric would be the better choice for MHs too. Basically you want electric for anything other than measuring the sun if you look at the chart in the link you provided.
Anyhow, here's some correspondence between myself and one of their application engineers instructing me that the electric calibration is best for the application. Also gives a nice description of the caveats of measuring LEDs. Very helpful guy.
Hope this helps
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Yes, the SQ-120 (electric calibration) would be our best option for your application. These units are sealed and submersible up to 30m and are compatible with salt water. The SQ-100's are considered self-powered and will generate a mV output that you can measure with your voltmeter. We calibrate everything to a factor of 5.0 µmol/m2/s per mV, so just multiply your mV output by 5 to derive the photon flux value.
In regards to measuring LED's with the quantum sensor, there are some caveats to doing so. The following link shows the spectral response of our quantum sensor (
Apogee Instruments Quantum Sensor - Spectral Response). As the graph shows, Apogee quantum sensors underweight blue light, and as a result, photon flux measurements for blue LEDs will be too low. They also overweight red light up to a wavelength of approximately 650 nm, above which they do not measure, and as a result, photon flux measurement for red LEDs will either be too high (if the LED output is all below 650 nm) or too low (if a non-negligible fraction of the LED output is above 650 nm). Additionally, LED's often have a very narrow spectral output, with a sharp peak of only a few nanometers. So, unless the quantum sensor has a perfectly flat spectral response, meaning it weights all wavelengths of light exactly the same, there will be errors. Electrically calibrated Apogee quantum sensors will likely provide a reasonable measurement for white LED's because they are broadband, and because electrically calibrated quantum sensors are calibrated under CWF lamps. However, for narrowband LEDs, like red and blue, Apogee quantum sensors will not provide an accurate measurement.
You can use the same spectral response graph (
Apogee Instruments Quantum Sensor - Spectral Response) to get a relative idea of the error. For example, a 450nm blue LED will have a relative response of approximately 0.8. Therefore, you can figure that the photon flux reading from the sensor is probably reading approximately 20% low. Just remember, this approach is only relative so give yourself a wide margin of potential error. A blue/white configuration should give you reasonable accuracy, particularly from the broadband spectrum of the white.
Hopefully, that makes sense. Please let me know if there are any questions.
Regards,
Jacob Bingham
Applications Engineer
[email protected]
Apogee Instruments
721 W 1800 N Logan, UT 84321
ph: 435.792.4700 fax: 435.787.8268
