Lighting For Marine Aquaria

WHY IS SPECIALIST AQUARIUM LIGHTING NEEDED?

Light is electromagnetic radiation of a wavelength that is visible to the human eye. The human eye can typically detect wavelengths between 400 nanometres (violet) to 700 nanometres (red). What we consider to
be white light is actually a combination of light at different wavelengths within this spectrum, with the intensities of the different constituent wavelengths determining its apparent colour.

As white light is formed by combining the wavelengths of the visible spectrum, its appearance can differ
from one source to the next. Colour temperature is used to describe the relative appearance of ‘white’ light
sources. The colour temperature of a lamp is determined by comparing it to the light given off by a heated ‘black body radiator’ (similar to heating a block of iron), the temperature in Kelvin(K) of the black body radiator at which it emits light that matches the hue of the lamp determines the colour temperature. A tungsten lamp
(i.e. a typical household light bulb) will have a colour temperature of 2,800K whilst sunlight is typically 5,700K and scattered blue light from the sky 10,000K.

By the time it has passed through the earth’s atmosphere the intensity of sunlight across the wavelengths of the visible spectrum approximates the curve below.

On a bright sunny day in the tropics the sun will typically illuminate a surface to 100,000 Lux (Lux is measure of the intensity of light over a given area). By comparison a typical fluorescent lamp in an aquarium will only illuminate objects at the water surface to 14,000 Lux. Because of this difference in the levels of light available for plants and corals in nature to those kept in an aquarium, specialist lamps are required.

Marine Photosynthesis

Photosynthesis occurs in both freshwater and marine aquariums, and so specialist light sources are required in both. However, in marine aquariums, the salt water absorbs light in the red part of the spectrum (see graph below), so invertebrates have evolved to utilise light at the blue end of the spectrum. Thus, specialist marine light sources with spectral intensities concentrated in the blue part of the spectrum are required to sustain marine life