These terms are often mixed up by readers of brochures and it is essential that a purchaser of a luminaire fully understands the terms as they are not only important in choosing a luminaire but may be informative indicators of the quality of a fitting.
CORRELATED COLOUR TEMPERATURE (CCT)
Correlated Colour Temperature (CCT) is a measurement of the colour appearance of a light source, expressed in degrees Kelvin (K). It is used to describe the "warmth" or "coolness" of the light, with lower numbers (2700-3000K) being considered "warm" or "soft" (orange) and higher numbers (5000-6500K) being considered "cool" or "daylight. (Blue)" . CCT is commonly used as a specification for lighting products. CCT is a way of standardizing the colour appearance of different light sources so that they can be compared and specified for various applications, such as lighting design, photography, and video production.
The appropriate Correlated Colour Temperature (CCT) for different lighting applications is based on the application, and other external factors.
Correlated Colour Temperature (CCT) for mining and industrial lighting applications should be based on the specific task and environment. As a rule of thumb CCT for underground and industrial lighting is between 4000K-6000K.
It should be noted that the human eye sees better under a higher temperature light than under a lower temperature light and hence for tasks requiring precision it is advisable to use a luminaire with a temperature in excess of 4000K.
It should however be noted that off the shelf luminaires are regularly supplied in a colour temperature of 6500K not because this is the best Colour temperature but rather because the base colour of a manufactured LED Chip is around 6500k and hence they are substantially cheaper than other Chips in the colour spectrum. Hence, it can be a primary indicator of the quality of a luminaire and why a product is cheaper when compared to others.
It is well worth reviewing an LED lights overall quality if supplied with a high spectrum value as it may also indicate overall quality issues.
CRI – (COLOUR RENDERING INDEX)
CRI (Colour Rendering Index) is a measure of the ability of a light source to accurately render the colour of objects compared to an ideal or natural light source. It is a scale that ranges from 0 to 100, with higher numbers indicating better colour rendering.
In LED lighting, the CRI is a critical factor that affects the perceived quality of light and the appearance of objects under the light. LED lights with high CRI produce light that is similar in quality to natural light and accurately render the colour of objects, while lights with lower CRI can produce a colour cast and make objects appear unnatural.
CRI is calculated by comparing the spectral power distribution of the light source to that of a reference light source and evaluating the colour shift of eight standard colour samples. The CRI of an LED light source can be influenced by various factors, including the LED chip efficiency, the type of phosphor used (for white LEDs), and the design of the LED package and optical components.
When selecting an LED light source, it is important to consider the CRI, along with other performance metrics, such as luminous flux, colour temperature, and efficiency, in order to determine the best option for a specific application. The CRI of an LED light source can also be affected by its operating conditions, such as temperature and current, so it is important to maintain proper thermal management to ensure consistent performance over time.
While different applications may not require a high CRI a specification sheet with a CRI below 75 should be carefully checked as it may very well be an indicator of the overall quality of the LED chips and the luminaire.
