| well as cerianthus was asking, the hood is typically a plastic cover that sits on top of the tank, on smaller tanks it will have one opening for feeding access etc, additionally it wil also provide a setting point for the tanks lighting.( generally fluorescent )
some tank hoods are an all in one design, and simply sit on top of the tank.
as to what light, well for visual appeal i would suggest somewhere in the 4500K + range, BUT that is personal preferance, some like a more pinkish tinge to their light. to see which you prefer try stopping in at the local big box hme improvement center, and check out their lighting center, they generally run a very wide series of color temps in a wide range of fixtures, you will note the higher the "K" number the "Bluer" the light. seen side by side the effect is very stark.
once you see a source you like, ask the person in that dept, what "Color" that bulb is, if he does not know, ask him to find out or make a basic guess,
Sunlight is in the 5000K range so 4500K is very close with just a hint of orange compared 5000k, a 6500k would appear bluer than a 5000k etc.
confused yet? if so my work is done... JK | 
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