tyler12345, to answer your question, you need to get right around 130-150 watts of proper lighting to grow anyhting you want without worrying about light. Go with the chart from gotdns. Find high light for each type and decide what lighting type you want to use. Get the lighing that you need that gives you the Wattage and Lumens you need. The Lumens calculations are broken down on the website. This will give you all you need to know to grow anything. You will want to get CO2 running as soon as possible. DIY is ok for the tnak but anyhting over 25-30 gallons really needs pressurized. If you don't want to mess with CO2 then go with moderate lighting or lower and buy plants accordingly.
The Kelvin rating is nothing more than the color rating of the bulb. True direct sunlight is 5500K or there abouts. For the purpose of aquarium plants, 6500K is the most used and most reliable Kelvin rating. It is extremely important to have the right but useless by itself. As for 18,000K lighting, to do with the brightness of the bulb. Only the actual color of the light.
It doesn't matter if you have the perfect Kelivin rating, the best CRI (Color Rendering Index) and the highest lumens for a single bulb. If you do not have enough wattage to provide enough lumens then all of it means nothing.
Until I see a better chart or better explanation I will use THIS
web site to determine what I need. I was produced by 4 top of the line fish keepers and is endorsed but at least 2 plant experts.
When it comes down to it, all the truely matter is Lumens. If you have enough lumens from the wattage in the right spectrum and a high CRI then you will grow the plants you want to. If you don't you won't!