That is because t5 lamps provide ideal spectrum for plant growth. Photocynthesis rates peak at 435 nm and 680 nm. A 6500k t5 has a spectral distribution with relative intensity peaks at 435 nm and 615nm. This equates to very little wasted light energy in terms of plant growth.hmmm that looks good. from what ive seen on this site it looks like the t-5s produce better plants than the t-8s. wish i would have gotten a few t-5 for supplimental light. good shit, ill keep watching for some bud shots in a few weeks