Yup, talking about the ambient temperature that they swim in / operate at. If your bulb is sitting in a garden whose temperature actually cools the bulb below its recommended temperature, you're not getting the lumens you think you are.

If, like in the case of T8's, they /do/, your garden and your lights aren't fighting each other. Then, just get the highest-wattage available, and stack'em And make sure yer aire temp comin' out is 75

In me own CFL garden, I used ta have the big 45w ones on the outside, and the trees of 26w on the inside...

... but the 200w equiv/45w actual 4100k 'shop lights' that were on the outside, are each now sharing one Y adapter from one 'all weather socket' that dangles
from a fixture above (two fixtures, four total bulbs) on the inside locations, and the outer two fixtures support a 'tree' of three Y adapters holding two 2700k 26w 1600lumen bulbs, and two 6500k 26w 1600lumen bulbs (eight total bulbs on two fixtures). Hmm... did I get my math wrong on a previous post? Yup, just checked it, gonna have to add a few more splitters and more bulbs to get up over the meagre 24,800 lumens in there

Gotta post a new pic, but I swear I'm getting some Sunbl4st3rs in there as soon as budget permits I just checked my cool friend Jeremy-dude's shoppe, and SB is claiming 2500 lumens for their new 26w bulbs, at the 6400k temp... I suspect their 2700k bulbs have a similar rating.

Support yer local Hydr0-stor3!