Correct me if I'm wrong but it wouldn't matter if your testing 2 3 or 4ft bulbs against the MH. Your not reading the par for the entire tank, just the area below the bulb.
Wouldn't testing an area between the two MH bulbs show something quite different for par? It wont change with the T5 over the length of the fixture.
My concern for a test like this is color temp and reflectors.
Scott
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