Uberhoust
Fish Herder
FYI Color temperature is not a very effective means of describing the output for LED or Florescent lights. Color temperature describes the mix of frequencies based on a theoretical perfect radiator, or black body. As the temperature of the objects increases it emits the energy, light, with a certain ratio of intensities and frequencies (wavelengths). Most incandescent filaments closely match the theoretical frequency distributions of the black body frequencies, and so for them the black body temperature (the color temperature, or the actual temperature of the filament) makes a lot of sense. The hotter the filament becomes the bluer the light becomes. Anyone who welds has seen the transition from cherry red, to red, orange, yellow, and white when running beads of molten metal, the color indicates how hot the metal is.
With other types of lighting the phosphors, or the LEDs directly, mostly determine the color temperature, the problem is that you can get "6500" kelvin colored light using as few as 3 different light frequencies. The light will look like 6500k light but might be entirely missing wavelengths that the plants need. These lights might look ok to people because the phosphors used are picked particularly for the human eye. This is where the RGB type lights fit, because they generate only three main wavelengths. Color temperature in this case is typically based on appearance, and because the color temperature was well understood from the incandescent lights it was also used to describe the type of whites that florescent and LED lights generate. The biggest point to note here is brand A 6500k might not be equivalent to Brand B 6500k.
The issue with color temperature is obviously known and now lights are often sold with two values given, the color temperature in degrees kelvin, and the Color Rendering Index. The higher the CRI the better the light. LED lamps with white, blue, and red LEDs are trying to get a good approximation of the "proper" color temperature, but also balance costs, they use a cheaper white led, then add the red and blue to make up the deficiencies in the white light spectrum and to partially skew the color temperature reading. The more expensive lights have multiple types of white light in them to make up these deficiencies, rather than one or two discrete frequency LEDs.
In our case we are worried more about the Photosynthetic Active Radiation, ie the light that the plants use. This is known as PAR rating. The PAR rating gives the amount of light usable by the plants, and the value given is directly related to the number of potential photons available at a distance from the lamp. Various literature suggests that a PAR rating of 70 to 100 at 12" is enough for most plants in a non-technical aquarium (ie no CO2). Not all lights will give this value, though there are phone apps that will measure this for you, (keep in mind that they are based on the sensor for the camera). It is important to note that the PAR radiation spectrum is based on land based plants but since most aquatic plants have terrestrial ancestors this is not a major hinderance.
In the end we have to use whatever metric is provided but it is good to understand the limitation of the color temperature. Some light manufacturers provide a wealth of data and others effectively just provide the light.
My rant is over and now you can go to your regular programming.
With other types of lighting the phosphors, or the LEDs directly, mostly determine the color temperature, the problem is that you can get "6500" kelvin colored light using as few as 3 different light frequencies. The light will look like 6500k light but might be entirely missing wavelengths that the plants need. These lights might look ok to people because the phosphors used are picked particularly for the human eye. This is where the RGB type lights fit, because they generate only three main wavelengths. Color temperature in this case is typically based on appearance, and because the color temperature was well understood from the incandescent lights it was also used to describe the type of whites that florescent and LED lights generate. The biggest point to note here is brand A 6500k might not be equivalent to Brand B 6500k.
The issue with color temperature is obviously known and now lights are often sold with two values given, the color temperature in degrees kelvin, and the Color Rendering Index. The higher the CRI the better the light. LED lamps with white, blue, and red LEDs are trying to get a good approximation of the "proper" color temperature, but also balance costs, they use a cheaper white led, then add the red and blue to make up the deficiencies in the white light spectrum and to partially skew the color temperature reading. The more expensive lights have multiple types of white light in them to make up these deficiencies, rather than one or two discrete frequency LEDs.
In our case we are worried more about the Photosynthetic Active Radiation, ie the light that the plants use. This is known as PAR rating. The PAR rating gives the amount of light usable by the plants, and the value given is directly related to the number of potential photons available at a distance from the lamp. Various literature suggests that a PAR rating of 70 to 100 at 12" is enough for most plants in a non-technical aquarium (ie no CO2). Not all lights will give this value, though there are phone apps that will measure this for you, (keep in mind that they are based on the sensor for the camera). It is important to note that the PAR radiation spectrum is based on land based plants but since most aquatic plants have terrestrial ancestors this is not a major hinderance.
In the end we have to use whatever metric is provided but it is good to understand the limitation of the color temperature. Some light manufacturers provide a wealth of data and others effectively just provide the light.
My rant is over and now you can go to your regular programming.
