Which T5 should I get

[Myka]

Originally Posted by Canadian

If you're going to calculate the T5 as if it's going on a 4 foot tank (54W) then you also need to be reasonable about the application of the MH - no one is going to try to realistically light a 4 foot tank with a single 250W MH. So consider that the above example is likely 2 x 250W MH in a real-world application (although that's purely speculation on my part as I wasn't the one making the claim - but it's certainly a reasonable consideration).

Secondly, very few people actually recommend running T5HO actinic lamps. A typical application would include lamps measured some where around 450nm but generally not pure "actinic" 420nm. And as an example even a 250W AB 10,000K on an M80 ballast has its largest peak at 420nm (actinic) so I suppose it's producing false high PAR readings?

Actually, LOTS of people run 420 nm bulbs...but the tendency is leaning away from it, yes.

You're still not comparing fairly. A 54w T5 is more intense than a 39w T5 no matter how long it (obviously) is. Just like having a 400w MH is more intense than a 250w. This is taking the same Kelvin bulbs into consideration though...for arguments' sake here. If you want to take the coverage of the bulbs, then you have to break down that 48" T5, and cover a 24x24" area with 4x54w T5 bulbs (breaking them in half to be 24x24"). Now, compare 4x54w T5 bulbs to a 250w MH. OR you have to compare 2x250w MH to 8x54w T5 to get the same coverage per 24x24" space as typical T5 spacing is 3". Comparing 4x54w T5 to 2x250w MH is hardly a fair comparison.

OR, you could try comparing it that way, but you would have a very complicated mathematical equation to figure out how many watts per square inch and PAR over the total useful area, and you would have to determine what PAR is considered usable, and wow that would be quite a chore.

Plus...it REALLY depends on what T5 and MH bulbs you choose, but even moreso for MH. You can get more PAR out of a 175w Iwasaki SE bulb run on an electronic ballast than half the 250w SE bulbs run off an electronic ballast. The amount of wattage actually used... Oh, and then you have reflectors to talk about too...

My point?? It is very difficult to give an ACCURATE judgement between MH and T5 by the average hobbyist. That's better left to the professionals. It's just better to realize that there are applications where T5s will be better than MH and there are applications where MH will be better than T5.