IT5 lamps are smaller in size (length and width) which makes T5's well suited for the low-profile, elegant fixtures that are especially popular for upscale retail, hospitality and commercial spaces like display cases or wall-washing. Its smaller scale allows for sleeker fluorescent direct/indirect surface mounted and pendant fixtures.
It should be remembered that the main characteristic that distinguishes T5 lamps from other families of fluorescent lamps is that they are designed to peak in their lumen ratings at 95°, compared to 77° for T12 and T8 lamps. This thermal characteristic provides higher light output in confined applications where there is little or no air circulation, and it provides more usable lumens per watt in indirect fixtures.
Fixtures for T5 can offer more uniform distribution (less "hot spots"), wider on-center spacing and shorter drop lengths for pendant-mounted fixtures. T5/HO
fixtures can use fewer lamps to deliver light levels similar to other fluorescent technologies.
Facilities have found applications for T5 HO
lamps in coves and cornices and in new direct/indirect fixtures, like the SIMKAR TDPW, designed to take advantage of the smaller-diameter lamp. Care needs to be taken to limit the use of T5 HO
lamps in low ceiling applications because this lamp is very bright and can cause discomfort from glare if not shielded properly.
Some industrial fixtures also use T5 HO
lamps, and the lamp is appropriate for many applications that require a high lumen-maintenance rating of 95%. This lamp only loses 5% of its initial lumen rating in the first 40% of its rated life.
I read this on another forum. Hope it helps.