When it comes to setting up a reef tank, lighting is a crucial aspect that every reefer should understand. In this article, we will explore the most important things about the science of lighting a reef tank that can help you create the ideal lighting conditions for your corals.

1. Lighting is Key

Believe it or not, lighting should be the easiest thing to get right in a reef tank. It may sound surprising, but the direct answer is that lighting plays a crucial role in the growth and well-being of corals. By providing the right spectrum of light, similar to the sun, and using a PAR (photosynthetically active radiation) meter to measure the light intensity, you can achieve optimal lighting conditions for your tank.

2. Why Horizon to Horizon?

Corals have evolved to be enveloped in light, not just from the directionality of the sun, but also from diffused light that comes from the sky. Without proper lighting, corals may cast shadows on themselves and their neighbors, leading to slower growth, funky growth patterns, and even death. In tests, it has been found that shadows can reduce PAR levels by about 75%. Therefore, it is essential to ensure that your lighting setup covers the tank from horizon to horizon.

Saltwater aquarium illuminated from end to end by Radion LED light fixtures

3. Creating Horizon-to-Horizon Lighting

To achieve horizon to horizon lighting, you have several options. One popular choice is a large fixture like a T5 or LED fixture that blankets the entire tank with light. Another option is using modular light strips that can be placed close together to cover the same area effectively. Additionally, medium-sized fixtures with ultra-wide lenses can also provide horizon-to-horizon lighting if placed at the right distance.

4. Emulating the Sun

Creating a lighting setup that emulates the sun is crucial for the well-being of corals. Corals have evolved over millennia in an environment that is bathed in a wide blue spectrum of light. Using lighting systems that mimic this wide blue spectrum is important to provide the ideal lighting conditions for your corals.

5. Creating a Wide Blue Spectrum

When selecting artificial lighting for your reef tank, look for LED lights that offer a wide blue spectrum. Wider is better in this case, as it provides a broader range of light that matches the natural environment of corals. Many lights will have a blue chart indicating the spectrum they cover. Ideally, you want a light that covers a range from about 390 nanometers to 470 nanometers.

LED light output blue light over a reef aquarium

6. The Importance of PAR

PAR (photosynthetically active radiation) is crucial for corals' energy production. Too little PAR can starve the corals, while too much can lead to excessive oxidant production, which can be detrimental to their health. For LPS (large-polyp stony) corals, a PAR range of 50-150 is recommended, while SPS (small-polyp stony) corals thrive in the range of 200-350.

7. Tuning PAR with a PAR Meter

To accurately tune PAR levels, it is essential to use a PAR meter. Relying on visual estimation is unreliable because the human eye is not sensitive to the blue range of light, where the PAR is concentrated. By using a PAR meter, you can measure the actual light intensity and make precise adjustments to ensure optimal PAR levels for your corals.

PAR meter measuring light intensity in a reef aquarium

8. Why Returning the PAR Meter is Better

Returning the PAR meter after using it for two months has its advantages. Apart from the monetary benefits, it ensures stability for your corals. Consistency is key for coral health, and by returning the PAR meter, you eliminate the temptation to constantly adjust your lights, providing a stable lighting environment for your corals.