460 or 420 actinics???

what is the difference between the 460 and the 420 actinics? i have a 75gal reef tank and i have two 460's and two regular 10k t-5's. what would i notice if i switched.

 

The difference is one bulb looks purple, the other blue. One is a true blue actinic which helps the corals growth and coloration, the other is for more of a "black-light" effect to pull out the bright neon colorations in some of your coral. Depending on the # of bulbs you have available in your fixture, you can put in just about any combo to create the right look you want in a DT, or the get the best growth in a frag/growth tank.

I sometimes get the two mixed up, but I think:
The 420 nm is for the "looks" (this is the purple-colored bulb),
and the 460 nm range is for growth (this is the bright blue bulb).

 

420nm

 

Bogie, I think you have them mixed up, the 420 is more blue and the 460 is more purple

 

I've seen the blue/purple switched depending on the manufacturer.
The ATI link below is for their T5 bulbs. Blue = 460, Purple= 420 nm.

Aquarium Technik Innovation ATI | New ATI-T5 lamps | ATI " PRO COLOR" and ATI "ACTINIC

And here for PC bulbs:
Current USA Compact Fluorescent Satellite Replacement Lamps Orbit Replacement Lamps Bulbs

you can see that the purple PC lights are listed as 420 and the blue bulbs are listed as 460.

Plus, I was a physics major... and I remember that the purple (almost ultra-violet) has a shorter wavelength than blue, and as the wavelength gets longer it moves out through green, yellow, orange, red, then infra-red with a longer wavelength than is visible by the human eye.

 

I was going off of ROYGBIV, with violet being at the end through to blue, green etc.

 

Yes, and violet (purple) has a shorter wavelength than blue. 420 nm is shorter than 460 nm.
So for what the OP was asking, the 420 will give off the 'cool flourescent colors', and the 460 will represent the natural blue light at ocean depth.

 

oops, you guys are right, sorry about that.