Is a light good for my fish tank?

It depends what type of fish u have. some fish prefer dim lighting or non at all however other like to have some light.

these examples are just some fish, obtusely there are other fish that require the same level of lighting

all piranhas like dim lighting

some tetras like medium lighting

not many fish like high lighting

i suggest u should have ur tank at low or moderate lighting

Yes, if you find the right kind of light which suits your tank (there are many different styles. Some give natural effects for example the sun and others are more of like a glow, if you understand what I mean..) although, if you have a lot of plants, be careful and watch out for algae as I found out myself..But as I was saying, get the right light, and you will appreciate the colours of the fish a lot more, and hey hooo, maybe your fish prefer a nice light.. :)

if there are no plants in your tank is not in an excessively dark room a light is not necessary.. It is nice tho because you will see colours in your fish that don't show if they are not 'reflected'.. to light my 35gal tank i only use 2 x 13w lights and i have very little problems with algae(note it get's NO DIRECT sun).. I give it a wipe once a week before i see any algae starting...

well, it sure makes it look nicer, and some fish even like it better. the only problem is that if you dont have a filter and snails, expect to have to wipe the walls of your tank every day for the green stuff appearing... the light makes it grow like crazy

only necessary when you are looking at the fish. If it's on more than a few hours a day, it will contribute to unsightly algae growth.

well if you have got warm water fish then yes plus it keeps your plants alive

it shouldnt hurt them unless the fish is deep sea