I have always heard to go with flat white paint for light reflectors. The reason the paint appears white is because it is reflecting the full light spectrum. The major difference between gloss and flat paint is that flat paint effectively diffuses (scatters) the light, where as gloss paint may directly reflect the light in straight lines from the angles of the hood. This will lead to something known as "hot spots" where some areas of you tank will receive more of the light than others.high gloss white spraypaint (aka krylon)
There reflectivity of both gloss and flat white paint should be similar, however flat white will more evenly distribute the light into your tank.
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