Lighting
Aquarium lighting
Light is the input most often over-supplied. A bright light over a tank without matching carbon and nutrients grows algae rather than plants. Six to eight hours is enough for almost any planted tank, and fish need no light at all beyond a day/night cycle.
Short answer
Light drives plant growth and algae growth alike. Duration and intensity are both adjustable, and reducing duration is the first lever to reach for when algae appears.
What it does
- Drives photosynthesis in plants
- Provides a day/night cycle
- Makes the tank viewable
Strengths and where it fits
Strengths
- Modern LED units are efficient, controllable and long-lived
- Programmable timers and dimming make photoperiod control trivial
Good fit for
- Planted tanks, matched to the plants chosen
- Any tank, for viewing and for a day/night cycle
Limitations and where it is the wrong choice
Limitations
- Manufacturer specifications are rarely comparable — lumens, watts and PAR measure different things
- PAR falls off sharply with depth, so a light adequate for a 30 cm tank may not reach the substrate of a 60 cm one
- Excess light is the commonest cause of persistent algae
Poor fit for
- Species that need dim conditions, unless heavily shaded with floating plants
Sizing
- Match the light to the plants, not the other way round. Low-light plants under a high-output light need shade, not more fertiliser.
- Start at six hours and increase slowly only if plants are healthy and algae is absent.
- A midday break in the photoperiod is popular and has no strong evidence behind it; a shorter total period is the more reliable lever.