LED manufacturing is not an exact science. If you do a production run of a million diodes you get a million diodes that are all a little bit different to each other. The diodes therefore go through a process called binning whereby they are tested and allocated to a 'bin' which is labelled in accordance with the Macadam Ellipse Steps.
The Macadam Steps
The Macadam Steps are a set of principles that were formed to show how the human eye distinguishes white colours. How that relates to LED is how closely matched the individual diodes are to each other in terms of the colours that you see. Simply, the lesser the number of steps the better the colour consistency you will get.
The majority of LED products on the market are typically binned around the 5-7 step mark. With a wide step LED, 5 steps for example, you would clearly see colour variation from lamp to lamp, whereas with a 2 or 3 step chip, little to no variation will be noticeable. As an architectural spec lighting manufacturer, ECOLED employs 2 or 3 step LEDs only in its products to ensure the perfect consistency.
CRI – Colour Rendering Index
CRI is a quantitative measurement of how accurate a light source can reveal an objects' true colour.
The CRI scale is 1-100 with 100 being daylight at noon on a clear day. The lesser the number, the harder it becomes to distinguish between colours, especially the likes of navy blue and black. To get the CRI of a light source, it is tested against a coloured swatch and each colour is given an R value. Each colour is given a percentage for each R value and the average is taken to reveal the CRI
R01 Light Greyish Red
R02 Dark Greyish Yellow
R03 Strong Yellowish Green
R04 Moderate Yellowish Green
R05 Light Blueish Green
R06 Light Blue
R07 Light Violet
R08 Light Reddish Purple
R09 Strong Red
R10 Strong Yellow
R11 Strong Green
R12 Strong Blue
R13 Light Yellowish Pink
R14 Moderate Olive Green
CRI in the 60's is satisfactory for cool white light in areas such as industrial storage but not suitable for residential.
CRI in the 80's is good and most commonly used for residential and most hospitality applications.
CRI in the 90's is excellent and typically used in high-end retail and medical applications.