Welcome to the fifth guide in the reef-pi series.

In this guide, we'll use reef-pi to automate a reef aquarium lighting. This guide assumes you have read through the first guide in this series, if not please go through it here.

Lighting is one of the most critical aspects of reef keeping. Corals feed on light. Although corals are animals (thus they cannot do photosynthesis), they have zooxanthellae (a type of algae) in their tissue that forms a symbiotic relationship with them. The algae provide nutrition to the host coral via photosynthesis, while the corals provide the entire habitat for the algae. Tropical corals can survive solely on photosynthesis, though they can also do filter feeding from the water column.

Light controllers in reef keeping are used to mimic natural reef environment. We'll be using reef-pi to automate the dawn to dusk daylight cycle.  Light controllers are also used during the introduction of new corals in the aquarium. Corals are very sensitive to changes in general, and when new coral is introduced in reef aquariums, it is helpful to set up proper light acclimation where light intensity is slowly ramped up to target levels, to reduce the new coral's stress and increase the chance of survival and reduce accidental bleaching.

Sometimes, moonlight or UV lights are used to simulate the lunar cycle. Coral spawning (sexual reproduction of corals by releasing spores) is closely linked with the lunar cycle. Corals contain fluorescent pigments which glow under UV lights. Often times, reef keepers will use UV lights for their viewing pleasure, outside the daylight cycle time.

In the reef aquarium, lighting requires a light source of a specific wavelength (around 460 nm) and intensity (50-200 PAR). Typically reef aquariums require 3-5 watts of light per gallon. There are a number of popular LED lights available for reef aquariums. It is also possible to build a light from scratch using appropriately chosen diodes (generally Cree or Luxeon). In this guide, we'll build a controller for one of the popular LED lights, Kessil, as the main light and an actinic LED strip for moonlight. Although the example circuits are for these specific lights, they should be fairly useful for a host of other commercially available light controls.

Due to the various requirements of light controls and diverse nature of LED lights, reef-pi's light control features are extensive compared to other reef-pi modules. To explore reef-pi light control features, we'll build a dedicated light controller as part of this guide. This controller will automate three Kessil lights (A80, A160, A360) as the main light source for the reef aquariums and a single moonlight strip from TrueLumen, which is mostly used for viewing pleasure, during night time when the main light (kessil) is off. This build is very much customized for my tanks, as shown below, but the technique should be fairly applicable to most other reef tank setups.