someone recently asked about helios t5 bulbs on my regular forum (cichlid-forum.com) and this forum was referred to so i decided to drop by and add my 2 cents to this thread.
i have 2 60" 80 t5 bulbs wired up to a fulham workhorse 7 ballast over my tank and have done quite a bit of reading on them. i would post pics but my imagestation account just ran out and i need to find another place to post them. now, back to lighting.
1. helios has a horrible track record with their pc lighting. do a search on reefcentral.com. i don't buy from companies with bad records period. no matter how great or cheap the deal.
2. although a 48" t5ho 54W bulb puts out a little more light than a 55W pc bulb (grossly ~5000 lumens vs ~4800 lumens respectively) the key difference is their ability to be reflected. what makes t5 so great is it's small bulb diameter. that unit does not have a good reflector and in fact is not suitable to even mount one. the reflector to use for t5 and some proof of it's efficiency relative to others is outlined here:
we are talking about multiples of increased light output which is unheard or with other flourescent bulbs. although done by the manufacturer their claims have been verified by others on reefcentral. what it means is that with the proper relflector you can effectively quadruple your light output. without the reflector t5's only advantages are saving space and longer bulb life but with the disadvantage of initial cost (around 20 for each individual reflector and bulbs between 20 to 40 bucks depending on length and make) and few bulbs to choose from (these will improve with time but may not ever approach that of t-8's and t-12's).
although "t5" compact bulbs give off nearly the same initial lumens because they are lined up next to one another they suffer from re-strike, a wide bulb which is difficult to efficiently reflect, and increased heat which decreases light output and bulb life. those who have switched from compact floro's to t5 on reefcentral have been blown away and atleast one member has used a lux meter which is reading off the chart (he has 8 t5 bulbs over a 180)
once again please refer to this link
for what makes t5's so special because without a nice reflector compact flourescents and t8's work just as well.
one awesome source for info on t5's is reefcentral.com which is where i learned most of what i have about them.