Evaluating Light

Natural daylight is a true “white” light. Its energy is balanced throughout the entire range of the visible spectrum. The value of a light source is determined by how well it renders all colors of the visible spectrum. Artists prefer the light from a natural moderately overcast north sky. Full-spectrum lighting is the most accurate reproduction of natural sunlight available, and accurate color rendition depends on it!

When selecting a lamp for a particular application, it is important to be able to predict its visual effect. The type and quantity of light emitted from a source affect the perception of colors rendered in it. Several methods of quantifying the color content of a particular light source exist to help predict this effect:

  • CRI Color Rendering Index (CRI)
  • CCT Correlated Color Temperature
  • Spectral Power Distribution
  • Tristimulus Values

When choosing lighting which will be used for accurate color analysis, two factors are considered primary:

  • Color Rendering Index (CRI); and
  • Correlated Color Temperature (CCT)

Spray Booth Lighting Success

KEY #1
Color-Corrected Light at the Right Temperature for color matching and blending

Light which falls in the range of 5000 – 6500 Kelvin

Using these evaluation standards, a full-spectrum light source is a bulb that has a CRI of 90 or above with a color temperature between 5,000 and 7,500 Kelvin.

Other common light evaluation methods are:

  • Spectral Power Distribution, and;
  • Tristimulus Values

These evaluation methods are used throughout industry to quantify colors of light, and to design light for a myriad of specialized applications.

The Color Rendering Index rates the light’s ability to duplicate the entire visible spectrum. The sun, for example, has a CRI of 100. Anything over 90 CRI is considered full-spectrum lighting.A lamp’s CRI rating is determined by comparing the change in color of a reference lamp. Eight standard samples are used for the comparison. The reference lamp and source to be rated must both have the same color temperature. A CRI of 100 indicates perfect color correlation. There are several manufacturers of “light booths” and multi-source lights that can be used as reference lamps in this form of color evaluation.

Color rendering is a measure of lighting quality. It is measured on an index from 0-100, with natural daylight and incandescent lighting both equal to 100. Lamps with a high color rendering index make objects appear more true to life. Plants can grow better with a higher color rendering index light source. But generally the higher the CRI the lower the lamp efficiency.