i am reading 5600 lux at the top of my canopy. what is the right amount of light at canopy level?
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5600 lux is not a big deal, begin to worry at 100 000 (the sun peak lux)+ lux for your 8 foot sq2 grow space @trizzle2011
However, a lux meter is calibrate for the sun spectrum and/or for white light, so it give you a partial spectrum reading from your Viparspectra 450 W.
None the less, It’s not with 5600 lux, even if it’s a partial spectrum reading, that it is too much… A good target in lux is 30 000 lux for a good and fairly fast and healthy growth… The minimum, for me, is 14 000 lux to achieve a fairly good harvest, imo…
Hoping that’s respond to your questionning, do not hesitate to ask further questions 
~Al 
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And here’s a good quantum meter that allow you to read the full spectrum, and read PAR. They are cheaper options but less reliable.
~Al
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I don’t think anybody makes a PAR meter with proper correction for most blue and red LED lights. They are really calibrated for sunlight. For example, you could have a very bright green set of LEDs and a PAR meter would give you a reading that says it is good, but your plants would die.
They do have corrections for MH, HPS, and fluorescent: All white light sources. Would probably be okay for white LED COBS because they have a pretty broad spectrum in the red. Not so for single-color LEDs. Might as well just use a lux meter. They cost about 1/10th as much.