11. How to convert aquarium light to LED?

So does color affect plant growth? Using standard (non-aquatic) fluorescents as specific examples, would using "cool white" lights (4000k) be worse / better / no different that using "daylight" lights (6000k)?

Aquarium Lighting Systems come in a complex array of options and varieties. Options include:

Light is essential to all living things, especially plants. There is a myriad of options for lighting your aquarium and proper lighting is an important factor in successfully maintaining a planted aquarium. Using the right color of light will create lush and healthy plants, and keep algae to a minimum. Your plants need a substantial amount of light to grow and this may require more lighting than what came with your fish tank. Choosing the fixture that fits your ideal fish tank will prevent you from re-buying.

12. How to set up LED aquarium lights?

Aquarium LED Light Fixture: Complete control of individual color LED's over a 24 hour period. Here is a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening.
I generally have the brightest lights on for about 12 hours per day, with 1 or maybe 2 hours of less bright or "ramping" up or down of LEDs if used. Sometimes with MH I will have them in a third cycle that is on for only abut 10 hours or less.

Despite commentary in some aquarium keeping forums, there is NO evidence that ramping up and down much longer than 1 hour where strong lighting is used provides ANY benefit to plant growth, fish, or reef environments (this is not applicable where one low to moderate lighting is used and one on/off cycle is all that is needed).
I have personally kept many aquariums (100s) going back to where only timers were all we had and used single time one for strong lighting, partial tank on with full lighting an hour later, and multiple timers. While have partial lights on for an hour did produce results over a strong on/off, multiple cycles made NO difference!
Think of it this way; in tropical regions, there is little difference in bending of light rays from the sun much past an hour after sunrise or an hour before sunset, so thinking a ramp up/down cycle much more than this time will make a difference has no practical or scientific evidence to back this up.

For LED moonlight settings, generally just a 1-5% of your full lighting power setting is sufficient between main lighting cycles.
If you have separate moonlights, I would run these 8-16 hours (I have yet to find in benefit from this that can be scientifically proven other than aesthetics).

ANY fluorescent light used for aquarium applications such as planted aquariums or reef, slowly burns up phosphors and other rare earth elements that produce the light energy necessary for PUR.
As with a UVC bulb/lamp used for a UV Sterilizer, these lights go through a "half life", meaning that a light that is run 12 hours per day that may last 2 years (as per rated life) should be actually replaced every year otherwise these lamps are running at 50% and less of initial light energy production and then often producing much more yellow light and even an imbalance of red that is inducing to more algae and cyanobacteria growth in particular.

The picture to above/left clearly demonstrates the difference we can see with just our human eye between new 6400K Daylight SHO and one nearly two years old.
The color temperature of the old lamp/light.

13. How to wire LED aquarium lights?

HID stands for "High Intensity Discharge", this technology is currently used in high end luxury cars, however there may be aquatic implications here in the future as PAR and other potential issues are worked out. HID lights use an electrical charge to ignite xenon gas (a colorless, heavy, odorless noble gas, which occurs in the Earth's atmosphere in trace amounts) contained in a sealed bulb. The technology of HID automotive lamps is similar to that of common vapor-filled mercury vapor street lamps.

14. How to use LED aquarium light?