Correct Aquarium Lighting
Aquarium lighting not only enhances the appearance of your aquarium, it also boosts the health of your fish, plants, and invertebrates. When designing a lighting system for your aquarium, you should try to duplicate – as closely as possible – the conditions in which your aquarium pets would live naturally. Thankfully, technological advancements in aquarium lighting over the past decade have significantly simplified the task of simulating natural conditions. This two-part article will explain the characteristics of light and discuss the duplication of natural light in fish-only, freshwater planted, and saltwater reef aquariums.
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Several factors including water depth, water clarity, weather, and air clarity affect the colour and intensity of light in natural aquatic environments. These factors, combined with varied overall water conditions between individual aquatic habitats, cause light spectrum and intensity to differ from one aquatic environment to another.
Understanding how aquarium lighting duplicates natural underwater lighting conditions requires one to understand of how these conditions are measured and analysed.
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Light Spectrum – Measured with the Kelvin Scale
The spectrum or “temperature” of light is measured in degrees Kelvin (K). The Kelvin scale describes the colour of a light source when compared to a theoretical “blackbody.” Think of a piece of steel that changes colour as it is heated. The Kelvin scale does not measure the light the steel gives off as it is heated; instead, it measures the colour of the light being given off. Colour temperature does not represent the temperature of the light source. It merely defines the colour given off in comparison to a blackbody radiating at the same temperature.
At 0 degrees Kelvin (equivalent to -273° Celsius), the theoretical blackbody emits no light. As the blackbody warms, it starts to emit red light. As the blackbody continues to increase in temperature, light wavelengths become more yellow, then turn green, blue, and lastly violet. A candle flame on the Kelvin scale has a rating of 1800° K. Sunlight at noon, with a Kelvin rating of 5500° K, is typically referred to as full spectrum because it contains a blend of all colours throughout the spectrum. Reddish light has a lower K rating and colour temperature, while bluer light has a higher K rating and a higher colour temperature.
As light passes through the first 15 feet of water, all the red and orange wavelengths are absorbed by the water, increasing the light’s K rating, and giving the light a bluer appearance. As the light penetrates to 30 feet, the water absorbs the yellow spectrum. And as the light reaches 50 feet, the water naturally filters the green wavelengths, leaving just the blue and violet wavelengths. This results in light with the highest Kelvin rating.
