First -- welcome to the wonderful world of finches!
Second -- how much lighting you'll need depends on the size of the cage, including how deep. Are you clamping the light to the side of the cage? If it's your only cage and you're not stacking cages, installing it on TOP would be far preferable. I've never liked the idea of my birds staring directly into a lamp affixed to the side. In their natural habitat they have overhead lighting, so also providing that in a caged environment makes perfect sense to me. Sometimes side lighting is the only practical option, for example if you have stacked cages. But otherwise I would think it's best avoided when possible.
Third -- please be aware that there is a longstanding debate whether UV lighting actually provides any benefit at all to birds. And both sides seem to offer rather compelling arguments, making it tough to know who's right.
I'm not sure there really IS a correct answer, as you'll find that there are very successful breeders out there using both methods -- with and without UV.
Fourth -- there are numerous other threads on this topic, and also are many FAR more knowledgeable and seasoned finchers on here than me! (I've only had my Gouldians for 16 months.) But before I adopted them I did devote quite some time to researching avian lighting needs, and even spoke with a couple of avian vets about it. Below, I'm reposting my explanation from a previous thread (rather than linking to it, because the topic wasn't even about lighting and you'd have to wade through too much other junk to find what you need
).
I know that many use CFLs and swear by them. I happen to use two 18-inch tube fluroescents instead (mainly to help spread-out the light rather than having it so narrowly focused), and use aluminum reflector hoods to help direct the light downward. Keep in mind, my cage is 30 inches x 24 inches x 36 inches deep....so you may not need as much lighting (or maybe you need more).
For whatever it's worth, here's what I decided seemed to make the most sense to me personally, on the 2 main considerations of cage lighting. Since I can't provide my birds with an outdoor aviary with access to natural sunlight, I've tried to mimic that experience as closely as possible.
1) UV: There is just too much conflicting opinion on this issue to know the truth. Some insist there is no real benefit at all, while others insist that birds critically need a UVA/B-emitting bulb when they're deprived of the sun's natural UV rays. But the birds apparently have to stay within 6-8 inches or so of the bulb to absorb very much UV, and the UV emitted apparently begins decreasing after six months or so -- requiring more frequent bulb changes than regular bulbs.
After giving it considerable thought and becoming more and more frustrated that there seemed to be no real clear-cut answer to this question, I finally had an epiphany! I realized: so what if the bulb doesn't provide a benefit by helping with Vitamin D production? Even if that's the case, I'm left with just a bulb that still provides quite good lighting. I'm not out anything, other than a few extra dollars. And IF the bulbs DO help the birds produce Vitamin D, then great -- that's a bonus! Why take the chance of possibly denying my birds that benefit, when I stand to lose nothing really by giving it to them -- just in case? So I opted to include one Arcadia 18w fluorescent as the 1st of 2 bulbs in a timed fixture sitting directly on cagetop. It claims to emit 2.4% UVB and 12% UVA.
2) FULL-SPECTRUM: Unfortunately, the term "full-spectrum" is widely abused, and often used as nothing more than a marketing gimmick. And while "daylight" bulbs are a far better choice than regular fluorescents, they still are nowhere near natural daylight in terms of correctly showing an object's true colors.
But there ARE a few truly full-spectrum bulbs out there, so I took extra care to locate the bulb with one of the closest possible matches for both color temperature and color-rendering index (CRI -- which refers to the quality of color light), as that provided by natural outdoor lighting. (As a point of reference, natural sunlight has a CRI of 100 at high noon around the equator, and a color temperature of 5,000K -- or 5,500K when both sunlight and skylight are combined.) As I understand, you should always aim for a bulb with a CRI of around 94 or greater, and a color temperature ranging somewhere between 5,000k and 5,800K. I found several fluorescents that met both these parameters, but there were 2-3 that were by far the closest matches. The one I opted for is the 17w Philips TL90 F17 T8/TL950. It offers a CRI of 98 and color temperature of 5,000K -- you really can't get any closer than that to natural outdoor lighting. Several other excellent bulb choices are listed here:
http://users.mis.net/~pthrush/lighting/kinds.html
This combination of both a UV bulb with a high-quality truly full-spectrum bulb seems to really make my birds' natural colors "pop" -- I've even had two different friends who've seen their photos ask if I keep the cage outside, because the lighting looks so amazingly natural. But the main thing is, I feel as if I'm providing them the next-best-thing to the great outdoors.
So....there you go. Probably much more than you wanted to know about UV lighting.
It really can become mind-boggling when you begin looking into it -- something I've vowed never to do again!
Good luck. Hope this helps.