MacAdam Ellipses, a fundamental tool in lighting technology, are named after a series of experiments conducted by physicist David MacAdam on colour and the perception of the human eye in the mid-20th century.
Although the human visual system is slightly different in each of us, the results of his vision research determined that it was possible to establish a colour match within a consistent statistical range within the MacAdam Ellipses.
What are they for?
Both colour temperature and colour rendering are factors that define the degree of quality of a light source.
However, in order to define the fidelity, uniformity and consistency of colour rendering, it is necessary to use tools capable of unifying criteria at a global level, and this is where MacAdam Ellipses play a fundamental role.
MacAdam Ellipses measure the possible variations that can occur in colour emission before the human eye is able to perceive them. This useful measurement tool detects chromatic deviations in light emission in order to be corrected and monitored for optimal and desirable results.
Thanks to this measurement system, manufacturers have been able to establish a general criterion for validating and quantifying the uniformity of light with respect to its colour rendering.
How are they calculated?
Depending on the colour to be achieved, a series of ellipses are drawn. Manufacturers of quality LED luminaires choose the types of luminaires that have the bin closest to the colour temperature to be achieved, thus avoiding chromatic variations in the same light source.
The importance of this finding allows lighting designers to choose a light source with all the guarantees. A correct selection of LEDs will ensure that the colour or tone of the luminaire is not affected.
When designing luminaires, it is important to take into account the standards set by ANSI -American National Standards Institute- which define up to eight nominal colour temperatures, each of which has seven MacAdam ellipses.
What is a MacAdam step?
Although our system of vision and colour perception is one of the most developed senses, tolerance to variations depends on the colour reproduced. Due to the physical characteristics of the human eye, our visual system is less able to distinguish chromatic variations in the colour green than variations in blue. Hence, the ellipse referring to the green colour is larger and admits greater variation than the one corresponding to the blue colour.
From this point onwards, everything that happens inside the ellipse of each colour will be indistinct to the human eye, with the limits of the ellipse being the critical points where the difference in chromaticity begins to be detected. These jumps produced are what we call MacAdam steps.
How are LEDs chosen?
In recent years, LED manufacturing has improved exponentially and manufacturers can now precisely control the resulting output colour. LED production is sorted by proximity to the centre point of the curve, resulting in varying quantities of each section.
When monitoring the quality of the chips in a luminaire, most of the output will fall within the less permissible ellipses, but there will still be LEDs that fall within the larger ellipses. The quality of these LEDs will therefore be higher in smaller or desirable ellipses.