I own an Apogee and a Uni-T lux meter. For most growers, I recommend against getting a PAR meter because a lux meter is sufficiently accurate and is 1/20 the price of an Apogee.
The PhotoBio is a lot less than the Apogee or even a SPOT On.
This paper done by the folks at Apogee might provide some insight. Sure, it's Apogee critiquing their competition but, if there's any doubt about their results, call Apogee and ask. They're very helpful.
If you really need a PAR meter and don't want to spend the money on an Apogee, I'd go with the SPOT On even though it's more $$ than the PhotoBio. I've never used either of them but the SPOT On looks like it will last quite a bit longer than the PhotoBio
If a grower just wants to check and adjust light levels hitting the canopy, a lux meter is sufficiently accurate. LUX meters also have an inaccuracy (5%±, just like the Apogee) and you have to use a conversion factor if you want to get to PPFD.
I've attached a document that lets you do the conversion from lux to PPFD. The conversion values vary because different lights put out different amounts of photons in the various wavelengths. So if you're using a lux meter you're going to have a little more inaccuracy that you'll have with a high quality PAR meter.
But that doesn't matter because the goal is to get light levels at about 800-1000µmols and then adjust light levels according to how much light your plants can handle.
Some growers like to know how much light their plants are getting. If that's the case and you're willing to spend the $$ to get the most accurate field instrument, drop $600+ for an Apogee with a case with the wand. But, for most personal/home growers, a lux meter will get you close enough and you can
fine tune your light levels according to how well your plants handle the light.
I specify the Uni-T and I would strongly recommend the Bluetooth model. The primary reason for that is convenience - the sensor is detached from the display and that's a great advantage in a lot of situation. IIRC, you can also get a wand to the Uni-T. That's great because it allows you to do things like put the sensor in the far corners of a tent and have it send the readings that you're taking to the phone. I use that info to figure out what parts of my canopy need additional light.
Below are the data from sampling 24 points on a canopy. The light is a Growcraft X3 flower light and the sampling grid was 6 sets of 4 readings that were taken back to front.
"128" is the standard deviation (a measure of variance) for PPFD, "5.6" is StDev for DLI.
That was a photoperiod plant in flower. The average DLI was 40 but that includes some spots in the corners and back of the tent.
This info is of, at best, questionable value to most growers so why go to the expense of 5% accuracy? For a Uni-T will set you back $32 and will do just fine for most growers.
