[StirCrazy]

simple. intensity will tell you how far you can penetrate, if tests are done properly you will see that light has 1 constant for the amount it decreases in intensity for a distance traveled.

so by being able to compare intensity we can determine the depth we will have suitable lighting at.

the T5s do have a bonus and that is uniform coverage, but that is at a cost. less intensity. it is the same as VHO, PC, NO ect.. as I have stated before a PC is brighter and more intense than a NO T5 as a PC is actually a T4, but don't get confused with the smaller tube size being better. that holds true for a given wattage. so we would have to relay compare a high output T5 to a VHO. the T5 will be better than the VHO, but I would guess by only 15 to 20%. the big advantage is size which allows you to put more wattage under the hood and a more even lighting.

But even this comes with a cost, with florescent tubes the smaller the size with the same wattage the more intense and the more heat that is produced, fluorescents main enemy is heat and as a result really impacts bulb life. as we saw one poster int hat post stated that they shift more red in 3 months so you should change the bulbs that often. so 4 changes per year compared to 1.5 for VHO/PC and 1 to .75 for MH. Also if you set up your MH properly you will get an average 2x2 coverage that will give you bottom PAR values than T5 with no problem.

the main difference is that lets say you have 1 T5 tube in say 14" of water and it has a bottom value of say 100 (just to pick a number) you now add 10 more tubes under that hood and you bottom value is still 100, just more of the bottom has that value. so you have not increased your intensity at all by adding tubes only the coverage which is a good thing, don't get me wrong. but now if you take that same 2x 4 tank with two good reflector SE MH you will find you have a bottom par of say 400 or higher (in relation to the other number) over 70% of the bottom and say 200 to 400 in 20% and 100 in 10%. over all the MH will pump a way higher average but it will not be evenly spread which is good also as it alows you to mix very high light corals with ones that don't like so much.

now having said all this we had a guy grow some colored SPS under NO's granted he had them high up and the growth was slow but they did have colour. so any light can work, it just depends on your overall goal and the method you want to take to get there. but changing 500 watts of MH bulbs once a year is a heck of a lot cheaper than changing 500 watts of T5 bulbs twice a year.

Steve