That is exactly why I put my first light the 600w cob with reflector cone on the meter I had read about alot of false claims without the bloom setting on it's only putting out 75w then I found the Chinese "1500w cob white light" I was very skeptical at first but it had great reviews all the other box fan cobs like this didnt come close to an actual 300w which I'm really impressed with I have a dr.meter lux meter but I know that's not very accurate thanks for all this info I'm definatley going to order a thermal gun and try to get a better idea of what's going on maybe a par meter if I can affoard it that way totally makes sense with the thermal probe this helped me alot I'll get more detailed info on the lights and take temp readings an get back to you see what you thinkMikesem420 good thing you measured actual power out of your lights. Those import fan box style lights often exaggerate wattage kind of like cheap stereos. Rate based on power potential of LED and not actual fixture power. Then how efficient those LEDs are is a different thing.
2 reasons to move your lights: 1) You can't dim your lights so you move it away to reduce par during veg phase 2) Heat at plant leaf
Best thing is to get a LED light that you can dim and then get light really close to plant and track the plant, this will improve your thermal load and longevity of the light and dial in the perfect amount of par. Then make sure you measure either with a spot probe or an infrared thermometer (looks like a laser tag gun) the temperature at your leaves.
Most credible temp data you find is based on leaf temperature and not ambient because in nature you can have colder ambient but warm leaf if infrared is intense because of altitude, time of day, time of year, etc. Kinda like all it matters is how warm you are and not the temp outside because maybe you have a space heater or a sweatshirt. So track plant temp because lights could be locally heating plant and room temp only tells you the temp at your sensor not your plants.
You will want lower PAR during veg and just about as much as you can get during flower to the point where you might need to supplement with CO2. The heights that are being recommended to you may work just fine but heights vary based the optics of the fixture (does it focus downward or shine at 120 degrees), how efficient your light is (600w of one LED may be a different brightness of 600W of another), and again temperature.
Best get a par meter. If you get a full spectrum white LED fixture you can sorta cheat with a flux meter if you get one dialed for LED and then follow what people are saying in the forums but you're best to get a par meter. Take a look at your PAR meter data sheet and make sure it captures evenly the PAR spectrum. For instance I use Apogee and their previous gen "LED" one dropped out on the red end of the spectrum so if you had a light that supplements at 660nm red it would not be picked up by the meter. I use their most current one.
Lumens is visible white light. Your eye favors the yellow white light and to some degree green which is why an equal power red and green light, green looks brighter. Its how we're programmed as humans. So white lights are on a lumen rating for how humans perceive. So if you have a lux meter (lumens on a surface per given area) and you have those blurple LEDs you can see how the lux meter will miss most of the light coming out of your fixture. This can give you confusing results between fixtures where brightness and performance don't correlate.
Nice! Optic will cut total light because it is filtering through a medium but will likely increase ppfd on your plants because a lot of it isn't wasted blasting the side of your tent. Good call.
and good luck with your first grow Mike.
