It depends on what type of
actinic bulb you are using, but some (like my T5 actinic +) actually has quite a bit of usable PAR....where as most
True Actinic 03 bulbs have very little usable PAR, thus only enhancing viewing pleasure.
I have read (don't remember which book) that corals actually need light in the 420nm range (actinic) but most daylight bulbs already have spikes in the correct range to suffice....
So my answer is, MOST actinics are nothing but visual enhancements, BUT Some actinics actually help the corals....
HTH a little.
Ohhh, and I agree to leave them on even if noone is around. Put your lights on timers and your corals will "learn" when its day or night....My brain always opens up just before Dark, It's amazing the corals learn the light cycle.
