It's really harder to compare them than I expected, the PAR goes up significantly as you get closer to the light... but then the coverage area obviously goes down. If you get far enough away, the reading "between" the fixtures is the same as right in front of one, if you get too close there's a dark area between them... but it depends how far apart the fixtures are.

So you might have to put the four LED fixtures closer together and closer to the plants to match the T5HO but use half the power?

It seems like these LED fixtures will work great, but I hesitate to say "X of the LED's would replace any other fixture exactly". I still want to test on live plants before I commit to hundreds of them.

If I get a chance I'll order 3 more LED fixtures (since I smoked one) and try to mount them to something that approximates the size of the T5 and T5HO fixtures.