That's because those readings are more accurate. All my plants in my garden, inside and out, reach and look towards the light. They are not fixed to looking straight up, why should the sensor?
I'm not denying that as a tool in your personal garden you probably should angle it. To have a fair apples to apples comparison of diffrent lights you have to use the same standard measuring techniques. The standard way to test a light for comparison purposes is to only measure with the sensor flat.
Yeah that is pretty weird, considering that Cree supposedly has LEDs that produce 303 lm/w http://www.cree.com/News-and-Events/Cree-News/Press-Releases/2014/March/300LPW-LED-barrier
Probably low bin and less than 90% efficient drivers.
303 lm/W LEDs are far from mass production.
Looks like it has COBs in it. Also seems to have a nice fairly even beam. I guess they must be 20 watt COBs because there's 12 of them. This video is a year old. I'm surprised Cree is still on that model actually. But yeah, the 303 lm/w ones are probably far from commercial production and that reading is also probably not what you would actually get from a lamp made with them. Those were probably ideal conditions. I don't know why SK is still using the older LEDs though, since these CXB high-bays are at least a year old now and apparently cheaper. SK is just not keeping up.
No those are cobs just not the largest ones 3070/3590. They make much smaller cobs.
Oh, okay, thanks for clearing that up. However, if you look at this video you'll see that the light is only at high enough PAR where the beams of the two cobs overlap. That tells me that you need to focus two cobs on the same spot at about 16-18" down so they form one bright round area of decent intensity. A single cob's beam is not suficiently intense. It would be less than 500 PAR, I'm guessing, since the overlapped area is about 980.
I still feel the proper use of cobs would be as others have stated in the the early DIY posts, 1 cob per 12-18" diameter of grow area
Okay but what's the par reading under one 82w (or whatever it is) cob's circular beam? I mean with no overlapping.
Good question, I thought someone had that data but I can't seem to dig it up.
Thank you for taking the time to do this testing. It is interesting that as the lamp is raised the average PPFD drops off, I assume this is due to scatter/absorption in the walls. Looks like 24" is ideal?
That's not the average PPFD - it's the average of the measured values. It isn't the same thing.
How do you calculate average ppfd?
Why would you NOT aim the meter at the light? The plants are going to turn their tops and leaves to face the light so logically you should do the same with the sensor. The readings should also be taken at the corners of the squares, not the middles (not directing these comments to you personally, SupraSPL, but whoever is doing the readings). We need to know what the intensity is at the outside edges of various sized grow spaces. Grow tents don't come in 2.5 and 3.5 foot sizes. Well they probably do but most people get the even foot sized ones I would think.