Which T5 should I get

[i have crabs]

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?

ive tested a few different setups, the 4 foot tanks i tested were under 2 250w's for comparison, the tek i have tested equall to a 400w even, the 400w was a tar ballast and not so nice reflector though, personally i hate how every t5 thread goes this way every time, im just stating facts that ive tested with my own par meter for my own knowledge, if anyone wants to listen great if not fine too my corals are doing great in a 27" deep tank with the light way higher than it needs to be so in my opinion tek lights work great, i havnt yet tested any higher end 48" t5 lights that would make a fair comparison so im still a bit skeptical on how much better the light output is on them, personally i think its mostly name and features like cooling and dimming that make the over double the price