There are several variables to consider when it comes to lighting. Three of them are “Kelvin, “Luminance’” and “PAR”. There are others but let’s start with these.
Kelvin (K) is a temperature scale used in measuring the color temperature of light. Lower Kelvin numbers indicate the light appears more yellow, while higher Kelvin numbers indicate the light appears more blue.
Lighting that has a Kelvin temperature of around 2700K is considered to have an "warm" or "soft white" color, which is what is found in traditional incandescent light bulbs. Lighting that has a Kelvin temperature of around 5000K is considered to have a "cool white" color, similar to what is seen in daylight or LED lighting. The ideal Kelvin light range for a reef aquarium is between 5000K and 14000K.
Luminance is a measure of the visible power of light which is perceived by the human eye. It is denoted by the symbol "L", and is usually measured in candelas per square meter (cd/m²). Luminance is useful for determining the brightness of a source of light, as well as for comparing various sources. It is also a common part of lighting design, as high luminance values can enhance contrast and provide a more pleasing aesthetic.
Luminance, or the intensity of light in an aquarium, is an important factor for any reef aquarium. Sufficient amounts of light can allow for proper photosynthesis and energy production for the aquatic organisms living in the reef. Bright and vibrant colors, for instance, will depend on the amount of light available for the corals and invertebrates. Inadequate light will cause reduced growth and result in bleaching of coral and other organisms. An ideal luminance range is from 20-50 PAR (photosynthetically active radiation). As well, brightness levels that flicker or change rapidly should be avoided as this can cause stress and other problems in the reef. By creating an ideal luminance level, it can have a great impact on the health and growth of the coral reef.
PAR (Photosynthetically Active Radiation) is a measurement of the intensity of light in the Photosynthetically Active Radiation spectrum, which includes 400–700 nanometer (nm) wavelengths. In horticulture and plant lighting, PAR is a metric for quantifying light that is available for photosynthesis in plants. PAR measurements are typically made using special spectroradiometers (spectromeeters) that measure the light directly or by estimating PAR from measurements of light at other wavelengths.
PAR (Photosynthetically Active Radiation) is a measure of light energy in the visible spectrum (400-700 nm) that is available for photosynthesis. PAR is important for reef aquarium lighting because the light provides essential energy for photosynthesis, which fuels the growth of the corals and other organisms like macro algae. The best PAR range for reef aquariums is around 100-500 µmol·m^-2·s^-1, depending on the type of coral/organism and its needs. Too much PAR can damage some organisms, so it is important to ensure that your lighting is not too strong for your aquarium.
