In each length of fluorescent tube there is only one wattage. If you need more light than that length provides, your only option is to use more than one tube. I live in the US where backfit lighting kits can be had for a reasonable price. They use various forms of compact fluorescent tubes and matching ballasts to provide far more light than a similar sized standard fixture would do. I have used a couple of backfit kits from AHSupply and found them easy to install and use. I also have set up some of my planted tanks using T-5 HO arrangements to good advantage. These are ways of increasing lighting levels by simply ignoring the standard tubes and setting up your tank for higher light options.
As we said up front, lighting is often a limiting factor for a planted tank but there are lots of options where you use low light and get good results. I have a 10 gallon tank with only 13 watts over it for the plants. What that tank uses is a simple 13 watt bulb, one of those twisted compact fluorescent bulbs that screw into an old fashioned fixture. The tank's plants are growing nicely and my total lighting investment is the price of that screw-in fluorescent tube. On the other hand I have a 45 gallon tank with 110 watts of T-5 HO lighting on it. It is a standard 3 foot fixture made by one of the specialists that sells to fish keepers and cost me far more than my 10 gallon lighting did. Both of these tanks grow pants about equally well but the 45 with over 2 watts per gallon of light will grow plants that simply die in the other tank due to a light deficiency. If I stick with low light plants, there is little difference between the 2 tanks. If I choose to go with plants that are more demanding, they grow great at 2+ WPG and do not grow well at all at around 1 WPG.
Each of us must decide what we are willing to spend on lighting when it comes to plants. There is more involved than the initial investment in a light fixture. A nice high intensity fixture will also burn through a lot more power in a month than its low light brethren. Unless you are determined to use lots of light regardless of the cost, I would suggest a low light / easy maintenance arrangement of plants that are comfortable in low light situations. Those plants can really shine in your tank and make you quite proud of what you have done without breaking the bank.
One easy way to judge the light and care requirements of plants is to simply price them. Let's face it, a plant that is undemanding and can thrive in low light takes very little effort to raise it. That translates in to a low cost / low priced plant. A plant seller will sell it to your LFS for a low price because even the low price is enough for them to make a profit. When a person at the LFS shows me plants, my first question is often what is cheapest. The cheapest plant is as often as not an easy care low light plant. I do check things but do not shy away from nice cheap plants. Those are often the mainstay of my planted tanks.
I also like floating plants. They are on average easy to care for and they often can get by on even less light than the cheap plants at the LFS. I use things like duckweed and frogbit to remove nitrogen from my more heavily populated tanks. Duckweed is reputed to thrive in poorly managed planted tanks, something that more likely than not describes my own. I am not a high tech person with lots of measuring equipment. That means that my approximation of plant nutrient needs is about as good as it will ever get in my tanks. If a simple duckweed or frogbit can remove the imbalance, I am happy. My tanks do not all grow duckweed equally well.
Some of my tanks grow duckweed like it was a weed while I cannot grow the stuff at all in other tanks. I find the situation similar in my frogbit tanks. My skiffia tank grows frogbit like a weed while all other tanks fail to be able to grow the stuff beyond the original population of plants. The skiffia tank contains Skiffia lermae and the fish are reputed to like water that is low in nutrients. I do not change water as often as some would suggest, so the plants serve a purpose of making the water nice enough for the fish. In the process, the plants prevent much evaporation of water from the tank since they form a solid cover of the water's surface. The tank is experiencing much less evaporation than other tanks right now, during the heating season.
My personal experience with riccia is not something that I would recommend. I have managed to lose every sample of riccia that I have bought over the years while things like java moss have thrived for me. It strikes me that riccia simply requires more light than I have in any of the tanks where I have tried it. Many people have no trouble at all growing riccia but its care has eluded me so far.
Please take anything that I say about plants with a grain of salt. I am not a plant person and have had trouble maintaining plants that "experts" find quite easy.
