20k is for a bluer color.
Often people use 14-16k for the best mix of color and growth.
But if color is more important to you.
20k then....well, then theres LED's.
Blue LED's crush anything else when it comes to bringing out color.
Every time people come by and see mine under the blues...well..."WOW" seems to be the most common response, followed by some 4 letter words of praise.