Quality and Color of Light
Color rendering
Color rendering describes the quality of light and is denoted as Ra (Europe) or CRI (US). The chart below shows a comparison between different light sources. Zumtobel uses exclusively LED modules and the majority of our products achieve CRI 80+ or CRI 90+.
Light color
The light color describes how “warm” or “cool” the light appears. Light color is measured by temperature in Kelvin (K). As shown in the chart below, a color temperature less than 3300 K indicates a warm white light, while color temperature above 5300 K is a very cool white light. Lower temperatures indicate warmer colors, while higher temperatures indicate cooler colors.
In addition to the colors of the surfaces, it is also the light color that determines a room’s basic atmosphere.
Color temperature and CCT
Color temperature (CT)
- Color coordinates of the Planckian radiator (Planckian curve)
- Real light sources often deviate from this: correlated color temperature (CCT)
- Judd straight lines: all points on these lines have the same correlated color temperature. This means that different color coordinates can have the same CCT.
White light quality and binning
In the production of LED chips, LEDs of different production batches have different properties with respect to intensity, color temperature, color location, or with respect to forward voltage.
The properties of each individual LED are measured after manufacturing and allocated to a group showing the same features. These correspond to finely differentiated parameters which are divided into so-called bins. Depending on the application and the product, these features are weighted differently.
By using specific binning groups, color and brightness tolerances – not just of the light emitted by individual luminaires, but also on visible luminous surfaces – are reduced to a minimum. Thus, illuminated surfaces and light emitting panels of luminaires are given a uniform appearance. This selection is especially important when it comes to “single LED” products and applications with maximum white light quality such as museums.
In practice, MacAdam ellipses are often used to give users an idea of how far individual LED modules differ with respect to color perception. MacAdam ellipses describe the color distances on the xy coordinates in the standardized color table. In theory, we talk about 1 MacAdam as soon as there is a visual difference with respect to color perception.
A color difference between individual LED modules of one luminaire and between individual LEDs, i.e. individual luminaires in case of spotlights, of 2 MacAdam ellipses is at present considered the maximum of technical feasibility. The color difference between wide-angle luminaires with high luminous flux levels (replacing fluorescent lamps) is considered excellent at 4 MacAdam ellipses.
