OK, let's stick to lighting on this thread Uriel.. let me try to paint the picture: (I'm making this up to try and explain what I'm thinking) as a beginner lets say you have 10 topics to master that play into this stage of the hobby for you. Each of those 10 topics might have 10 to 100 bits of info or skill processes that some of us know of. Transferring between 100 and 1000 topics to you in a meaningful way in a short period of time is pretty much impossible, lol.
Lighting is important to the fish in the sense that most higher level organisms have evolved to operate their biological machinery with the clock of the earth's rotation involved. Lighting can also be very important to the visual image of our tank, one of the main points to having the whole hobby. But really, the lighting/fish relationship is not one we worry about nearly as much as the lighting/plant relationship. Lighting is a major controlling factor for us when we work with live plants and deal with the algae.
As mentioned, we can break our thinking down into 3 aspects: light quantity, light duration and light spectrum (which is really just light quantity broken down into all the frequencies/colors.) Light duration is the easiest topic but one of your most powerful tools. We've already hit on this I believe: you need at least 4 hours of continuous light to get the photosynthetic machinery going in the majority of our aquarium plants so that they are actually making some useful sugars (food) for the plant tissues. The total hours will fall into the same ranges as the hours of days in various parts of the globe where the plants come from and for the various seasons - so you can picture a big range from 4 to 12 or so hours and this things -do- make a difference once you really get in to planted tanks, but for beginners the main lesson is that duration is the big tool in dealing with algae usually.
Light quantity and light spectrum are trickier topics with more information needed for understanding I believe. Let's mention quantity first. You can read in wiki about how photosynthesis works of course but we all know the photons go in there and provide the light energy to the plants. The history of talking about "amount" of light in our aquarium hobby world is basically a mess. Its all bound up in the fixed efficiencies of the old T12 and T8 mechanisms that were around for years and falls apart when other mechanisms are used. The "guidelines" were created just for these T8 type systems: somewhere around 2 watts per US gallon and below was said to be the "low-light" methodology range and above that was said to be the "high-tech" methodology range (each of these methodologies constitutes an entire set of techniques for success with a heavily planted tank.) This all falls apart if you use T5 or incandescent or metal halide or LED of course because the electrical systems driving these may have very different efficiencies and remember that our original "guideline" is based on power instead of a light measurement, quite unfortunately. (the lastest stuff being talked about among the plant experts at the AGA conference I just attended involved electronic sensor you hold down under the light.)
Hopefully we'll discuss light quantity more but one of the bottom lines is to realize that a T5 of a given wattage will give off a lot more light than a T8 of the same wattage - they have different efficiencies. All these different light types also have different "directionalies" in practice. Light emits off a fluorescent tube in a perpendicular circle, radiating out and so a lot depends on the reflector. LEDs are highly directional and dependent on their reflectors as are the big hot lamps used in marine setups. Why is directionality important? Well, one reason is that a lot of light can pour out of the *sides* of the tank and the taller the tank the more of that that happens!
Let's mention spectrum. On a practical plant growth level, the importance of spectrum gets exaggerated a lot in our hobby. In many ways light is light is light as long as plants get enough of it for a correct period of time. But in the end there are things to know. Plants mostly use red and blue spectrum areas to grow and there's lots of blue out there in bright sunlight in the ocean where lots of algae and bacteria grow at high rates. That's all I'll say about that at the moment. Spectrum -does- matter a great deal to how our tanks look, how our plants and fish look. In the freshwater planted tank world, 6700K is a good starting point but often combinations of different colored tubes will end up creating the most pleasing look in a given tank for a given aquarist. (Hey, I'm aware this is crazy long for a beginner post but I just wanted to give you a glimpse into the complications of where us "explainers" are coming from, lol, and why its so hard to talk about it at least for me in a given post.)
So where is the most middle-of-the-road place for beginners before they really figure it out? Perhaps T8 tubes of 6700K at 1.5w/g running for 8 to 10 hours inside a highly reflective reflector with the plants being dosed with liquid carbon and the macro and micronutrients figured out to be either the fish waste or small supplements that are kept under control by weekly water changes (a thing I'd call "reduced EI low-light technique".)
~~waterdrop~~
