How can I use color temperature and color rendering measurements to determine what kind of lighting I need?

Color temperature and color rendition are among the important factors that affect the appearance of a lighted area and the things within it. These factors can help to evaluate the type of lighting needed for particular lighting tasks.

These terms describe two different characteristics of lamps. Simply put, color temperature refers to the color of the light source itself, while color rendition refers to the relative appearance of colors of objects under a light source.

Correlated Color Temperature (CCT) at its most basic level is usually described as “warm” (yellowish) or “cool” (bluish). It is conveyed as degrees Kelvin (K). Warm light has a lower CCT than cool light. A warm light that has a typical yellowish glow has a color temperature of around 2700K. A cool light that has a typical blueish glow has a color temperature of around 4100K.

Color temperature affects the appearance and feel of a lighted space. Higher (or cooler) color temperatures are brighter, closer in appearance to mid-day sunlight. Lamps at these levels are best used for reading or other tasks. Lower (or warmer) color temperatures are softer and are better used for mood or area lighting.

Color rendition refers to how accurately colors appear under a light source. Color rendition is measured by the Color Rendering Index (CRI) which is a range from 0 to 100 with 100 representing the most accurate (or natural) color characteristics. Lamps with lower CRI values can indicate that some colors may appear unnatural when illuminated by the lamp. A good rule of thumb is to use lamps with a CRI of 80 or for accurate color rendering. A CRI of 90 or higher is considered excellent.

Tasks that would require a high CRI lamp would be anything that requires close inspection, such as examining paint color charts. Another would be for illuminating television or movie sets.

Lighting tips:

• For the most accurate comparison purposes the CRI should be used to compare lamps with the same CCT.
• Unlike in the past, fluorescent lamps can now be considered part of you decision now they are available with CRIs over 90.
• Use lamps with the same CRI and CCT ratings to give your lighting a more uniform appearance.