Correcting for the Spectral Errors of Common Electric Lights
Because of the increased popularity of the reefkeeping hobby, the reef tank lighting market has recently grown exponentially with hundreds of lighting options now available. Unfortunately, all types of electric lights have a unique spectrum, and therefore also yield a unique set of spectral errors when measured by any commercially available PAR meter. These errors are generally minimal and shouldn't be a concern for most aquarists. However, when high precision is required, the following information, and a little bit of math, can help.
In response to emerging electric lighting technologies, Apogee has done extensive research to help customers make accurate PAR readings. Spectral errors for different commercially available lights were determined via the method proposed by Federer and Tanner (1966). These results are found in the table below.
The spectral errors of common lights such as CWF, CF, MH, and HPS are fairly straight forward. To make a high precision PAR reading for these types of lights, simply recalculate the PAR reading given by the meter with the corresponding percent error from the table below to yield a more precise PAR measurement
In recent years, LEDs have gained popularity in the marketplace due to their low power consumption and minimal heat output. This is great for cost savings, but due to the unique spectral output of the various colors (for example, very narrow wavelength ranges), LEDs present a challenge when attempting to make accurate PAR measurements. With commercially available PAR meters, certain colors of LED tend to read high, while others read low. The best device for accurate PAR measurement is a spectroradiometer, which provides intensity readings at each wavelength. However, these are often not well suited for underwater measurements and can range in price from several thousand to tens of thousands of dollars.
When used properly, the MQ-200 offers a very reliable and economical solution for precisely measuring the PAR output of LEDs. To achieve the highest level of accuracy, simply recalculate the PAR reading given by the meter with the corresponding spectral error percentage from the table below.