Simulating Natural Light With LEDs

To enhance visual comfort for building occupants, evaluate color rendering of LED lighting choices.

By Sally Lee, LC and Rich Rattray
From the April 2020 Issue

Natural light remains the ideal light source across the wide variety of facilities. It delivers true colors and feelings of comfort and calm for building occupants. When the sun goes down though, or in areas where natural light is not an option, previously these benefits were lost for building occupants.

Natural light color rendering
(Photo: Dmitriy Moroz)

Now, facility executives turning to LEDs can deliver clean, natural light by placing proper value on color rendering in their lighting choices. Color rendering is an important element of lighting performance used to beautify spaces, facilitate interpersonal communication and well-being, and accurately present colors. With LEDs, there are new ways to evaluate and predict color performance, and its ability to produce color “recipes.” This is thanks to the growth of broad, balanced color or “full” spectrum lighting products that deliver excellent color rendering. The results are visual spaces with vibrant, accurate, natural colors and reduced eye strain for building occupants—all achievable at a minor incremental cost in an LED upgrade.

Color Basics

To value color rendering, we have to understand the relationship between light and how the eye sees color. For an object to be seen as being a certain color, that color must be present in the light striking it.

When we say “color” in light, we are really talking about a wavelength of visible light energy. Visible white light is made up of a series of wavelengths that combine to make white light.

With daylight, we have a broad, balanced spectrum that makes colors appear naturally, or how most people would expect them to appear.

With electric lighting, the traditional goal was to produce white light efficiently by focusing energy on the fundamental primaries red, blue, and green. Different spectral distributions result in different color rendering abilities and color appearance of the light itself, both of which can have a profound effect on human color perception. People, objects, and spaces under one light source can look very different than under another.

Color Rendering And LED Lighting

For 55 years, the lighting industry used a simple metric to describe how well a light source renders colors. Called the color rendering index (CRI), it is a measure of lighting fidelity, in this case how well a given light source renders a series of eight pastel reference colors, numbered R1 through R8, compared to an ideal reference source.

Natural light color rendering
When natural light is not an option, either due to time of day or building layout, facility executives could soon offer occupants the benefits of natural light with broad, full spectrum LED lighting products entering the marketplace. (Photo: LEDVANCE)

The higher the average CRI, the better. Traditionally, a CRI of 80+ was considered “good” for a majority of commercial general lighting applications, while a CRI of 90+ was recommended for color-critical applications such as hospitality, retail, healthcare, and graphic design.

CRI was never a perfect metric, and the advent of LED technology accentuated its flaws. As a result, you can have two light sources with the same CRI but that render colors with a noticeable difference in how colors appear. A significant area of concern was how well CRI for LED sources rendered saturated reds (R9, an optional additional color not included in CRI but available for testing), which research suggests is a critical part of human color preference. This resulted in some lighting manufacturers beginning to report both CRI and R9 for their products.

Another response was the Illuminating Engineering Society’s publication of TM-30, a proposed method for color evaluation designed to report more information with greater accuracy. TM-30 offers a color fidelity measure similar to but more accurate than CRI, and another expressing color saturation.

So, which is better? CRI does work for many basic general lighting applications, particularly when supplemented with R9, and remains referenced in codes and standards. TM-30, however, is superior when color is important to the application, whether it’s decor, well-being, how people appear when interacting, or merchandise. The greater the value placed on these, the greater the value of being able to accurately evaluate, predict, and select the right lighting.

Color Application

LED upgrades are typically driven by a perception that light is a commodity to be obtained at the lowest cost. This places an emphasis on energy efficiency and energy cost savings, which is appropriate but should not result in missed opportunities to cost-effectively add value. While light is indeed a commodity, lighting—the application of light to spaces—can be an asset, supporting organizational goals by providing accurate colors, visual comfort, and enhanced space perception. These are worthy investments that can produce tangible value, and at a minimum should be considered in facility lighting decisions.

A sensible approach is a broad, balanced color spectrum like natural light, which remains the ideal light source. LED lamps can now offer “full spectrum” illumination, with a highly engineered spectrum that closely matches natural light. With this capability, consider lighting products that:

  • control blue wavelengths to avoid eyestrain;
  • properly saturate red to make spaces and flesh tones both accurate and vibrant;
  • do not oversaturate red, resulting in a sacrifice in energy efficiency; and
  • provide a broad spectrum without sacrificing light output or adding significant cost.

When upgrading with LED lighting, facility executives should focus on energy savings while asking, “What does lighting need to do and what can it do for this space?” Anywhere color is important—whether facilitating interpersonal communication, ensuring occupant well-being, supporting merchandise sales, or other goal—take steps to ensure the right lighting is installed. These steps include using precise and accurate color metrics to evaluate products, searching out LED products that can deliver a broad and balanced spectrum that imitates natural light without sacrifice in cost or efficiency, relying on reputable manufacturers that back their claims, and, whenever possible, installing a mockup to see the major difference the right lighting product can make in color perception.

Working with the right partner, facility decision-makers can find broad, balanced color or “full” spectrum lighting to bring the benefits of nature inside facilities.

Lee, LC, is business development & special projects manager and Rattray is technical specification manager at LEDVANCE LLC, the makers of SYLVANIA general lighting in the United States and Canada. In North America, LEDVANCE LLC offers a wide range of SYLVANIA LED luminaires for various applications.

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