lighting for clones

during the cloning process, i've switched from 2 regualar flourescents of 40 watts each to a fixture with 6 compact flours, 54 watt each tube. couple of questions, what's the consensus on light cylcle: 24 hr straight or 18-6? i've read info insisting it's better to go 18-6 because that's what the mamas were on and the cuttings, even the cuttings need a little time to rest and transfer sugars. however my neighborhood grow store proprietor with the coast to coast attitude swears on the 'lights always on until roots kick out' policy. any ideas?

second ?
about these 6cfi's, they are stronger and there are more of them., 6 instead of 2. obviously the lumens are greater. any hints on how high they should be from the tops of the clones? i'm running an aero cloner that is 4' long and 2' wide, not that the machine's dimensions figure into the equation. i worry about buring my babies and i want to give em the best exposure so they will root 'lo mas pronto possible'. i don't have a light meter to measure the outputs. again any ideas?

thanx in advance for everybody's input.

I recently found a great fluorescent tube to use with cuttings, Zoomed ReefSun. It's a combination of a full spectrum phosphor and actinic blue so it's got a lot of the light use primarily for vegetative growth. Helped my clones out a lot. You can get it at PetCo or PetSmart etc...