The package says T4 so I am assuming it is. Its not a spiral twist on type, its got 4 pegs on the bottom to plug it in. The only difference I can seem to gleen from info online is that they are brighter than normal CFL and they are also to be used with dimmer switches (normal CFLs arnt) and that you have to buy ballasts for them, they dont come on the bulb. Maybe I am wrong, but I have some 42watt T4 CFLs and their lumen output is over 3000, compared to some of the regular screw in CFLs around here at about 2200-2700lumen for 42watt. They look similar to these lights but are not the same brand Just showing pics so you know what I mean with 4 pin base. 42 Watt T4 Compact Fluorescent GX24Q-4 Base, Compact Fluorescent Plug-In Triple, Compact Fluorescent, Bulbrite CF42DT/E/830-42W DIMM.EL.TRI.AMAL.30K The only drawback I can find is the ballasts for the bulbs I have are 30-50 bucks a peice and the lights anywhere from 7-30 a peice. Basically wondering why these arnt used more often for growing? Or is it a normal CFL with just some extra crap added so its dimmable? The lights are the right spectrum for flowering, more lumen output than similar CFLs and I have a bunch. Comments appreciated as these lights are odd and hard for me to lookup because I dont know much about them. Thanks!