TM-30 and the Evolution of High Color Rendering Testing for LED Light Bulbs

Light-emitting diode (LED) technology has revolutionized artificial lighting due to its high energy efficiency, long lifespan, and versatile form factors. Among the diverse types of LED products, high color rendering LED light bulbs are specifically engineered to produce light that closely mimics natural daylight, enabling more accurate perception of colors.

The primary metric used to evaluate color accuracy in lighting has been the Color Rendering Index (CRI). CRI, first published by the International Commission on Illumination (CIE) in 1965 and revised in 1974 to include chromatic adaptation, uses a scale of 0-100 (100 equals perfect rendering) based on testing how well a light source renders eight pastel colors against a reference (daylight is the benchmark). The need for a color rendering index corresponded to the increased use of fluorescent and HID lamps.

Traditionally, a CRI of 85 to 90 indicated sufficient color rendering for most general lighting applications. For color critical applications – art galleries, museums, high end retail – a CRI of 95 became the standard.

Beginning in the early 2000s, the growth of LEDs used for “white” lighting applications in interior spaces revealed CRI’s limitations – nuances in LED spectral outputs were not captured in the traditional CRI testing. The addition of special test colors (R9-R15) and the development of newer metrics led to the TM-30 standard that provides enhanced evaluation of LED color rendering.

TM-30 Specifics

• TM-30 uses 99 color samples for the Fidelity Index (Rf) compared to CRI’s limited set. This provides a much better overall test of color rendering.
• TM-30 includes the Gamut Index (Rg) to show color saturation (vividness) to identify if colors look dull (low Rg) or excessively saturated (high Rg).
• TM-30’s Color Vector graphic shows specifiers how different colors affect aspects of the application. For example, it shows how reds affect the natural appearance of skin tones.

Here is an example from a manufacturer spec sheet of the color metric for a specific LED MR16 lamp:

While TM-30 offers the specifier a more detailed, accurate picture of color rendering, its complexity means CRI is still published by manufacturers because of its familiarity for most buyers. CRI provides a single number making it an easy to understand reference for the majority of lighting decisions. In addition, many building standards, government regulations and utility efficiency programs require a minimum CRI for lighting products to comply.

For professional lighting design purposes, TM-30 is the essential standard.