Guide: How to properly plan aquarium lighting

Lighting does not just determine how your aquarium looks. It influences plant growth, algae development, the behavior of many fish, and the level of maintenance required. Anyone wanting to plan their aquarium lighting with the help of a guide should therefore not start by looking for the brightest light. What is crucial is that the light, tank size, planting, and stock are well-matched.

Planning aquarium lighting: Thinking from the tank upwards

Everything begins with the length, depth, and height of the aquarium. A light must illuminate the entire length of the tank effectively without becoming significantly dimmer at the edges. For a 60-cm tank, this is easy to solve. With long panoramic aquariums, deep tanks, or custom dimensions, however, the lighting requires more planning—for example, through the use of multiple lights or modular, combinable LED bars.

Tank height is frequently underestimated. In a shallow aquascaping tank, even a moderate LED light reaches the substrate well. In a 60 cm high aquarium, light rays lose their effectiveness significantly on the way down. Ground cover and light-hungry plants there either require more light output, targeted positioning under the light, or less demanding plant species.

The cover and design also belong in the planning process. Under a closed lid, the light, mounting, and heat generation must be compatible. Open aquariums offer more freedom in the choice of lighting, but increase evaporation. With custom-built tanks, it is sensible to coordinate the lighting directly with the cover, cut-outs, and access for technical equipment.

How much light does the aquarium need?

Wattage alone is of limited help with modern LEDs. Different lights convert electrical power into usable light with varying degrees of efficiency. For practical purposes, information on lumens, light distribution, design, and controllable channels is more meaningful. Even more important remains the question: Which plants are actually intended to grow?

A community aquarium with Anubias, Java fern, Cryptocorynes, and mosses copes well with low to medium light. Such plants grow more slowly, require less fertilizer, and are more forgiving of beginner mistakes. For many classic freshwater tanks, this is the low-maintenance choice.

Medium-intensity light suits densely planted aquariums with stem plants, Vallisneria, or colorful accent plants. Here, the demands on nutrient supply and regular maintenance increase. Strong light is primarily of interest for demanding aquascapes, carpet plants, and intensely colored plants. It offers creative possibilities but also accelerates every mistake: if CO2 or nutrients are lacking, algae will often utilize the light faster than the desired plants.

High light output is therefore not a quality feature for every tank. Those who prefer to work without a CO2 system or maintain only a few robust plants are often better off with a moderate, easily controllable light than with a very bright model running at full power.

Light color: A natural appearance instead of colorful effects

For a freshwater aquarium, a neutral to daylight-like spectrum is suitable. It renders fish, plants, and hardscape clearly and reliably supports most aquarium plants. Warm white light often makes roots and reddish tones appear particularly cozy, while cooler white creates a clearer, fresher impression.

RGB and multi-channel LEDs allow for individual settings. This is practical for aquascapes and display tanks, but should not tempt you to use very blue or strongly colored light permanently. For the plants, a usable overall spectrum counts, not the most spectacular color effect possible. A subtle morning and evening mood can improve the view, but it does not replace a good main light.

Setting the correct lighting duration

To begin with, six to seven hours of light per day is a reasonable guideline, especially in newly set up aquariums. The tank must first stabilize biologically, plants must take root, and filter bacteria must find their place. Starting directly with ten or twelve hours often creates good conditions for algae before the plants have properly grown.

In a mature, well-planted aquarium, eight hours are sufficient for many setups. Nine hours can work if CO2, fertilization, and maintenance are balanced. Longer is not automatically better: plants also require a dark phase, and more lighting time does not solve poor plant growth that is actually caused by nutrient deficiency, incorrect water flow, or too little CO2.

A timer or integrated control removes the uncertainty from this task. Light should be switched on and off at the same time every day. A midday break is occasionally used to adapt the lighting to the daily rhythm. However, it is not a reliable remedy against algae and is unnecessary for most tanks. Consistency brings more than changing lighting times.

Plants, CO2, and fertilizer as a joint system

Light is the engine of plant growth. The stronger the lighting, the higher the demand for carbon and nutrients usually becomes. Therefore, a light should never be planned in isolation. A bright planted tank often requires a CO2 supply, balanced macro and micro-fertilizers, as well as regular water changes.

With low to medium lighting, a tank can also look very attractive with simple fertilization and without a technical CO2 system. Slow-growing plants, epiphytes on roots and rocks, as well as well-thought-out substrate create a calm, natural image. This is just as sensible for beginners as it is for anyone wanting a stable tank with manageable maintenance effort.

Strongly lit aquariums are not inherently complicated, but they require a fixed routine. Plants are trimmed more often, nutrient values must be monitored, and the light intensity adjusted if necessary. Dimmable LED lights are particularly practical here, as the output can be increased gradually after the setup phase.

Taking stock and ambient light into account

Many fish benefit from structured, not-too-harsh lighting conditions. Floating plants, tall stem plants, roots, and shaded zones provide security for cautious species. This is especially true for tetras, dwarf cichlids, or labyrinth fish. A very bright, completely openly lit tank, on the other hand, can appear restless and makes shy animals visible less often.

Direct sunlight on the aquarium glass should be avoided. It leads to strong fluctuations in brightness, can heat up the water, and promotes algae in the event of unfavorable nutrient levels. Bright daylight in the room is not a problem as long as the sun does not fall directly into the tank for hours.

For a saltwater aquarium, different requirements apply. Depending on the species, corals need a significantly more intense and spectrally different light. Here, special reef lights, controllable blue light components, and settings adjusted to the corals are necessary. Freshwater LEDs are usually not the right solution for this.

Avoiding typical mistakes in lighting planning

A common mistake is switching to a stronger light as soon as plants grow poorly. Check beforehand whether plants are adequately supplied, whether they have been chosen to suit the location, and whether the water flow transports nutrients to them. Light reinforces existing conditions—both good and bad.

Equally problematic is new, very bright lighting over an aquarium already suffering from algae. First reduce the lighting duration or dimming, remove algae mechanically, and address the root causes in the system. A complete blackout can help in individual cases, but it is not a permanent maintenance strategy.

Also, pay attention to maintenance. Splash water, limescale deposits, and dust reduce the light output. Clean cover glasses and light housings regularly, always with the power supply switched off. With LED technology, replacing bulbs is significantly less necessary than with older fluorescent tubes, yet it is still worth checking for declining brightness and the proper functioning of the control system.

Terboven Aquaristik offers lighting solutions for compact beginner tanks, planted community aquariums, and demanding special formats. Particularly with long, deep, or individually planned aquariums, it pays to select light length, mounting, and covers together from the start.

It is better to plan the lighting one step more calmly than to permanently overwhelm the tank. A dimmable light of the appropriate length with a clear timer gives you the opportunity to observe the plants and stock accurately—and then adjust the light specifically to the aquarium.