You know I never really did understand why people said if they have 20k's they don't bother with actinics. Whereas, if you were using 20k's I would expect you'd need actinics more than if you were using 10k's.
I have been doing some reading/research and have gathered info.. 10k's are high in the violet spectrum of light, while 20k's (as well as 65k iwasakis) are high in blue light. Regular PC blue bulbs (fake actinics) are full of blue light as well, but true actinic 03's are very high in violet light. So infact if you were shooting for a full spectrum of lighting, and you were using a blue bulb such as 20k's , you'd want to supplement with a violet bulb. Following that guideline, I have heard people with a mix of 20k and 10k mh bulbs over their reefs get amazing colors. BTW, although iwasakis produce a yellow light, they are high in blue light (as well as green/yellow light), but they are a bit lacking in other spectrums such as violet light.
- mike