Which T5 should I get

[Canadian]

Originally Posted by Myka

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.

HUH?

Real world application time here:

We're talking about measured PAR over an aquarium when using typical installation methodologies with T5 and MH.

54W T5HO lamps are 4' long. When lighting a 4' tank with T5s most people choose 54W T5HO. The benefit of the T5s being that you can cram many of them beside each other with individual reflectors. This is not something you can readily do with MH. So, with the MH over a 4' tank the best option for coverage is to use 2 bulbs with a nice big reflector like a Lumenarc to provide optimal coverage and intensity.

All this comparison of with respect to square inches of coverage is ridiculous. We're talking about the real world application of the technologies and the fact that they were actually measured in a typical application.

The comparison of 8x54W to 2x250W MH made previously was simply showing that in a real world application the T5 example produced better PAR numbers under those circumstances (which were pretty typical installations and applications). Myka, you were the one who suggested that the watt for watt comparison was unfair but you made some errors in your calculations. Now you're looking for another ridiculous way to compare things - have fun with that.

The bottom line is that a well designed T5 fixture produces comparable PAR values to typical MH applications and ultimately the decision is up to the consumer to weigh the pros and cons of each technology given their desired application. The MH camp on this forum has been making some ridiculous comparisons and unsubstantiated nonsense about how T5s produce less PAR and about how some how actinics produce false PAR readings (I call BS).