LED and Light Quality
While LEDs do not have a full color spectrum, we must pay special attention to their color quality and color rendering capabilities.
LEDs may contain less red wavelengths which can cause poor rendering of red colors. It is possible to avoid this by using special materials when producing the diodes. This is why one must pay special attention to the LED’s color rendering index (CRI) which is often expressed as Ra.
When LEDs are produced, they are formed with many different colors or color temperatures. The International Commission on Illumination’s (CIE) color diagram is used to create a binning structure, i.e. groups of diodes that share the same color characteristics. LED suppliers offer different bins of LEDs to luminaire manufacturers. The fewer bins the higher cost.
Some binning systems relate to the human eye’s color sensitivity via a model called MacAdam ellipses. The ellipses are mapped onto the binning structure in the color diagram and their size corresponds to the LED’s color tolerance. The size is measured in steps. The more steps, the bigger the tolerance and the easier it is to spot a difference in color. Generally, a 3-step ellipse is considered a good color tolerance. Most Luxo luminaires comply with a 3-step tolerance.