What I've read is Lux meters look at the full spectrum and grow light's primamrily push out the PAR spectrum. This makes them inaccurate. What I find them good for is consistancy. I cant afford a par meter but I do have a lux meter which I use less and less BUT it does allow me to get in the ball park. I hoep that makes sense. Best of all is to watch your plants. I like to see the leaves reachin up just a little towards the light but not stretching too much.