Need some bulb help

[Tstone]

Currently have 2 48" Aqua Glo lights T8.. both 40 watts..

I want something a little bit "stronger", or brighter.. Most lights are rated by the x,xxxK or something like that, like 10,000k so i'm super confused and have no idea what I need...

Can anyone tell me what are some bulbs I can get that will be (preferably MUCH) brighter?

 

[Tstone]

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[joe jaskot]

Here is a good read on choosing lights for aquariums: http://www.aquariumguys.com/diy-aquarium-lighting.html