Great advice, the uni-T is a game changer if you can't afford a apogee or whatever, I wouldn't trust phone apps to measure light levels, and I never remove leaves if I don't need to. Those big lower leaves always let you know what's happening to your plant, I've defoliated photoperiods and I think that benefits them but with my autos I leave them be. Here is two lemon ak autos at 11 weeks and I'd be in a world of shit if I removed any leaves throughout this grow. And I learnt pretty quick to keep the tent door closed when dialing in ppfd dli etc
Nice looking plants!
Re. Uni-T vs the Apogee. Even if the Apogee isn't a signficant expense, the only reason I'd go for it is that it makes it really easy to sample a canopy. In addition to the Apogee, I bought the Uni-T for testing/learning, and then bought the Uni-T BT model to see how they'd incorporated BT.
The nice thing about the Apogee is that it has a sample mode which allows me to move the sensor in various places around the canopy and then press a button on the handset to record the PPFD. It is more accurate than the Uni-T, probably, but it's also 20 times the price so, even if someone is flush, I'd
probably recommend the Uni-T instead of the Apogee.
What was a bit of a letdown was that Uni-T didn't do much with the BT model besides adding BT. I was hoping that they'd add a logging feature but instead, they just added the ability to set a sampling frequency and the ability to create a download file. I tried it out about a year ago and was left wanting. On the other hand, the price stayed the same and so it's
1/20 the price of the Apogee.
Re. keeping the door closed - if that's the case, do you set the sample rate to 1 every few seconds? And, I agree about open vs closed. For my "front row" it works out to about 100µmol. What difference are you seeing in readings?
Re. phone apps - my thinking is that as long as you set them up right (use a diffuser on the iPhone) and can calibrate it against a known good source then it should be OK. Unfortunately, the tests that I've seen, with the exception of Photone, show that some of the apps have varying levels of accuracy for different light levels. That' very no bueno. When I tested Photone, it was 16% high but at least it was consistent. Given that you have to use a paper strip (an absolute kludge but it's needed for under stable reasons) or spend the $$ on a diffuser, I'd rather just get a light meter and use a crib sheet to convert to PPFD. Or just think in terms of lux. Either way works.
One thing that hit me a few weeks ago — a light meter will tell you how much light is hitting you canopy but only your plants can tell you how much light they can use. That's why I'm not all that hyped up about getting an Apogee even if a grower has the disposable income.
I was an artillery officer so I'd describe using a meter as light adjusting fire. You get the first round into the area and then move it left or right and "add" or "drop" a certain distance. A light meter is very similar to that. Even with an Apogee, you're setting the light to a certain level but only the plant can tell you just how much light it can use.
"world of shit if I removed any leaves throughout this grow." - and RIU has a great acronym for that. I chuckled the first time I saw "LTFA" and it's just so true!