That means if you had perfectly even light distribution over (1)m2 the sensors readings are going to stand and be true anywhere in that (1)m2. But.. if you shined a laser in that same (1)m2 and took a measurement with that sensor underneath the laser, that sensor will still say that the corners of the (1)m2 are getting tons of light, and will also say that on average that (1)m2 is producing more μmol than what it really is. So.... If you don't have uniformity the sensor is going to be inaccurate at describing a true quantity of μmol/m2.
Before I begin I want to say thank you for providing a detailed and educational response to this thread as you seem to be one of the only members here with sufficient knowledge on the subject to form such a reply. You're helping me to understand where the separation is between your methodology of determining grow light efficiency and the data I use to build lights. I'm beginning to understand now the response to the figures I've posted, as they were never indicative of a meter squared area or taking readings at a meter from the source. They were simply relative data sets for comparison purposes only.
No point-source light distributes light evenly over an area. Light will always have the highest reading at direct center beneath a point-source fixture. Intensity will always lessen as you move away from center. Since we are talking about point-source lights here, even distribution is not a question of
If, it's simply not possible. The edges of any point-source fixture will never match the intensity directly beneath the LEDs.
The sphere isn't light proof so that's kind of a big deal.
The sensor placement is not correct.
The sensor is averaging a point reading to m2, so without a multiplier you'd at least want your sphere inner surface area to be 1m2.
Light proof or not, zero is zero. The video shows 0 umol before the LED is turned on.
This integrating sphere (8" diameter, 0.13m2) was created specifically for building precise, quantum-balanced spectral ratios to know relative umol output from one wavelength to the next. It is not representative of a 1 meter squared area, nor was it built to calculate a umol/joule/square meter/second reading. Yes the numbers would be drastically different in a 1m2 sphere. At a distance of 1 meter at direct center in an open atmosphere environment, you'd probably get a reading of 1-6 umol from these LEDs (perhaps I'll do this tomorrow for fun). But I do understand now why you and others have stated an "impossible" response to my numbers, and am grateful for you taking the time to better explain how to create umol/joule data (a new concept I've been trying to understand). My data of umol per watt is only applicable to the specific integrating sphere being used and is a measurement without multipliers to compensate for a 1m2 area. Data which was only ever used to calculate spectral ratios.
Just to be certain I'm understanding you correctly (with sensor placement aside) - to get the umol/joule number you're after we would perform this same test in a 1m2 (11.125" radius) integrating sphere. Correct? Now the next question I have is whether you'd like to assist in designing one?
