How much stress is normal when switching to flower lights?

I veg. under 150 watt (40 real watts I think?) compact fluorescents, one per plant, generally 24 hour lights on schedule.

I use Sun Systems LEC 315's to flower. I generally keep them in veg. (24 hours lights on) for the first few days or so after moving into my flower tents to let everything fill out a little, get adjusted, etc.

The last couple strains I've done have gotten REALLY stressed out when I'm moved them over to the 315's.

Any thoughts as to why that might be happening?

I move the lights way up so there's a good 2' of space above the plants (as opposed to the 16" I hang it at normally).... Nothing else changes but the lights... All other conditions are pretty much optimal (temps/RH/watering/nute schedule)...

Is it possibly just because some strains can't handle the intense lighting on 24 hours? That's really the only thing I can think of, so I'm going ahead and switching to 18/6.

Anyone have any other suggestions?

Thanks

They only need 18 on and actually require some dark to fully process the light.

That cmh is potent compared to tiny and weak cfl. Are you also potting up in the switch? That could also very much stress the plant.