How is light quality measured?

Lighting systems must provide the right amount and quality of light for a given task. Quality lighting is not too dim or overly bright. Instead, it provides uniform lighting without producing a glare.

There are three primary methods for measuring light quality:

  1. The Color Rendering Index (CRI) measures the ability of a light source to reveal the color of objects, compared to natural light. CRI values range from 1 to 100, with light sources at <45 providing poor color rendition. Light sources with CRI values >75 provide sharper, crisper, and more natural colors.
  2. The Visual Comfort Probability (VCP) is defined as the percentage of people that will find an environment comfortable with regard to visual glare. Glare is a product of high differences in brightness and can cause annoyance, discomfort, or loss of visual performance. With VCP scores from 1 to 100, a VCP of 65 indicates that 65% of the occupants would not be bothered by direct glare. Typically, schools require a VCP rating of 70 to 80.
  3. Color Temperature indicates the color of a light source. While many lighting options are available in a range of color temperatures, the most commonly used and recommended temperatures are warm white, cool white, and daylight. The right color temperature for a given environment is dependent on the task and level of natural light.

At Performance Services, we always complete a mockup of a typical area before proceeding with an LED retrofit. This allows occupants to experience the light levels and ensure they are appropriate before we proceed with the installation.

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