There are a lot of different lights to choose from. The kelvin rating is what tells you if there is more blue or more yellow etc. To make it even more confusing different brands of the same kelvin rating and same wattage can look very different. Your best bet is to look around at people's tanks and if you like their lighting go with that. Different kelvin ratings also produce different growth rates. 10k is generally the fastest growing but some people don't like the look so they either go to a higher rating or add actinics or both.
If it were my tank I would probably go with 6 10k and 2 actinics but that is just my preference and after trying it I could change my mind.
