[chandigz]

20000k bulbs don't look as bright because of the large amount of blue they produce. Your eye sees blue as less intense/bright then yellow or red. Your white t5 will appear to over power them as they produce more yellow and red light. I find14k produces an nice iceblue white light (I prefer these you get a nice colour and brightness)and 10k-is like daylight-white with a hint of yellow they will look the brightest(I find these a little to yellow for my liking). If you have a lot of t5 then i'd go with 10k halide (will give you better shimmer/brightness)and use some of your t5 (blue 460nm, actinic 420nm, purple/pink) to get the colour you want and the other t5 (10k, 12k, 14k) for added brightness). Hope this helps.