OK, let's talk about lighting a bit. Again, in an attempt to just relay some basic things I'll no doubt be passing along things that are not the latest ways the planted hobbyists would approach them but I hope some of the information may be better than not knowing of it.
Obviously, plants must have light to perform photosynthesis and grow and be healthy. Light is extremely important to the balance of an aquarium. Light is the engine that powers how fast the whole plant system is working - if the light is bright then the plant "revs up" and in doing so, consumes a lot of other resources like carbon, nitrogen, phosphorus, potassium and many other things. If the light is lower the plant is not consuming so much and if the light is out then the plant may consume some of the things it would normally produce! So light is a big "control" factor in a tank with plants.
Planted tank hobbyists have historically ended up with a number of interesting "approaches" or "methods" of running a tank and achieving a type of look. I'm only going to describe two (very simplistic) of these. The first is called "high-tech" and the second is called "low-light" and these are just names that have happened to stick but are referring to ways of doing things.
The traditional dividing line between "high-tech" and "low-light" is at about 2 watts per US gallon. So, for example, if you shine 30 watts down on a 10 gallon tank, you are at 3 w/g and doing high-tech, whereas if you shine 10 watts over the 10 gallon you are at 1 w/g and dong "low-light" technique. The fact that "watts" are used in this simple old guideline means that only light bulbs of a particular efficiency were under consideration and if one uses more efficient bulbs then the guideline really needs to change. The guideline was envisioned with fluorescent bulbs of 1-inch diameter (T8 bulbs) in mind, among others. Often, newer bulbs such as T5 bulbs, are sold in configurations that give off more light for a similar wattage.
The difference between high-tech and low-light (lets call them HT and LL) is a big deal when you are running an aquarium with plants. As you get in to the HT range and push your plants with more light, they need more plant nutrients (plants use 17 elements as nutrients) and one of them, carbon, can be very difficult for you to provide and them to get! Carbon is provided by CO2 and submerged plants are at a huge disadvantage compared to emergent or terrestrial plants because CO2 is available in water in only a tiny fraction of its availability in air. In other words, plants on land can get lots of CO2 quite easily, but plants underwater get hardly any. This is why you may have heard of fancy planted aquariums having big CO2 tanks as part of their equipment.
If you stay down in the LL range under 2 w/g then you can use plants that are used to growing in low-light situations and have them stay healthy even though you have less light and no extra CO2 provided. This LL technique is very popular with lower-cost and beginner freshwater aquariums, whereas the high-tech technique with bright lights and extra CO2 equipment is very popular for beautiful but expensive planted-tank setups. Another popular thing that has happened for LL technique is that new chemicals have been developed that allow LL hobbyists to help out their carbon situation by dosing "liquid carbon" products directly in to the tank, rather than via the (better) CO2 apparatus.
And its not just carbon, although that is the hardest, there are lots of the other 16 elements that the plants need that the aquarist has to attend to by providing "fertilizers" of sorts and not letting them become too concentrated in the tank.
I'm sorry that was so long. Its just a few first comments about the "lighting skillset" I talked about in a previous post.
~~waterdrop~~
