The MacAdam Ellipse
The MacAdam ellipse or SDCM, which is an acronym for Standard Deviation Colour Matching, shows how LEDs belonging to a specific production line can deviate from standard values in their colour consistency. However you prefer to word it, it's crucial to lighting projects as slight colour differences in the appearance of LED light can ruin an effect. Imagine looking at a hotel from outside and noticing that some of the balcony lights were a different shade or asymmetrical lighting in a glamourous shop window or even off-kilter lighting in a dark corridor. It matters and matters a lot and tempting as it may be to buy bulk discount LED's, you will almost certainly regret it and end up spending twice.
David MacAdam conceived the MacAdam ellipse in 1931; he experimented with the perception of the colour of the human eye and the chromatic differences detected based on the type of lighting and then transferred this data into a CIE chromaticity diagram, now known as the MacAdam ellipse.
The MacAdam Steps, (SDCM), are steps for measuring colour differences in the appearance of LED light. Values were standardised to understand how much the illumination of an LED light has a faithful colour rendering. It was found that the points inside a 3 Step ellipse are indistinguishable from each other by the naked eye.
1 Step MacAdam: no colour difference
2 Step MacAdam: differences visible only with tools
3 Step MacAdam: subtle differences for the human eye
4 Step MacAdam: visible colour differences
5 Step+ MacAdam: strongly visible colour differences
The ANSI (American National Standards Institute) standard recommends that the colour value has to be located in an ellipse within four threshold units, however, most manufacturers use 2 as an average.
Generally, for better project results you would typically use step 2, and we strongly urge you to always use step 2 with symmetrical lighting. However in many instances step 3, can also be acceptable because, as stated, you cannot easily distinguish any difference with the human eye, but we don't recommend going any higher than step three if you are looking for quality as by step 4, you will be able to notice the difference.
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