LED Lighting Systems


Color Matters

A Practical Guide to Color Science in an LED World

A new look at the science (and art) behind professional lighting

Color science serves as an underlying technical foundation for the entire lighting industry. It establishes a consistent way of thinking about light—how it is created, controlled, and delivered in real-world implementations. A core understanding of the science of color is critical to lighting professionals, who must be able to specify the right light—color, technology, luminaire, and more—clearly and accurately. Only then can they achieve their unique vision, whether designing lighting for a home or an iconic architectural gem.

The impact of LED lighting on color science

Our understanding of how color is perceived and measured has changed over time, based on new discoveries, new color models, and evolving light sources. As with any disruptive digital technology, the introduction and market dominance of LED lighting renders many of the old ways of thinking about color obsolete. It also introduces extraordinary new capabilities, exciting opportunities, and new applications that were unthinkable, unaffordable, or impossible just a decade ago.

But the move to LED technology also creates confusion. Lighting professionals now have to deal with new underlying approaches to color that go beyond the familiar RGB—including RGBA, RGBW, and other multi-channel luminaires. They have to stay in sync with evolving standards. And they have to choose from a broad array of system components—including luminaires, controllers, and sensors.

As a visionary that helped lead the LED lighting revolution, Philips has a unique perspective on color science and deep knowledge of all aspects of lighting. We created Color Matters to provide lighting professionals of all types with a brief, easy-to-read guide that delivers:

  • an overview of core color science concepts
  • an exploration of how color science is  changing in the LED era
  • an overview of Philips technologies that  maximize performance and consistency
  • general guidance for specific lighting  scenarios

Traditional Color Science

How is color perceived and measured?

Man-made light is created for humans to perceive, appreciate, and benefit from—at home, work, and in public space. How we interpret and understand color involves the human eye and brain, which translate light into color perception. Light receptors within our eyes transmit messages to the brain, which produces the traditional, familiar sensations of color.

That's the simple description—the more detailed version is even more remarkable.

 

Why is color so complicated?

Color is not inherent in objects—
our eyes only perceive color in reflected light.

This fact reveals some of the core complications of color and light, since light will vary depending on the surface that reflects it. And our physical perception and interpretation of light varies from person to person. In short, perception of light and color are subjective, not absolute.

How do we
perceive color?

Important (and truly amazing)
facts about color perception.

Color
preference

Why do we prefer certain lighting
sources and colors?

How is color
measured?

Some of the ways light is measured
via scientific quantification.


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How is color perceived?

A full exploration of the complicated (and truly amazing) biological origins of color perception is beyond the scope of this brief guide. But these facts are important to know:

Since people have different percentages of red, green, and blue cones, they may perceive color—and differentiate hue—slightly differently. Since color perception is, ultimately, a construct of the brain, the signals to the brain will vary, making it impossible to compare color images that different people see.

Rods and cones comprise the key types of photoreceptor cells in the retina of the eye. Rod cells function in less intense light. Critical to peripheral vision and night vision, rods are concentrated at the outer edges of the retina. There are more than 90 million rod cells in the human eye. Cone cells are responsible for color vision and function best in relatively bright light. There are about six to seven million cones, concentrated towards the macula of the eye.

Cultural differences and personal preferences affect color perception.

Some people (8% male, 1% female) experience some form of color perception impairment.1

Blue-heavy white light sources have a higher perceived brightness, if the lumen values are the same.

The reflectance of the object (e.g., a wall) also impacts color perception, since it affects the amount of light/color that actually reaches the eyes receptors.

A MacAdam ellipse is the term used to describe the point at which a color difference becomes just perceptible to the average person viewing in a laboratory setting.

At very low light levels, people cannot perceive any color—only black and white, a phenomenon known as scotopic vision (vision of the eye under low light conditions).

As proof of the power of light, color light has a significant effect on the human sleep/wake cycle.

Perception of light also changes as the eye ages, creating the need for light sources to change and adapt to accommodate aging, as well as personal preferences.

And as if color wasn’t complicated enough for an average person viewing, consider color synesthesia, a condition where a person perceives letters or numbers as inherently colored. Or chromesthesia, where sounds can trigger the perception of color.

Understanding the foundation

It’s helpful for today’s lighting professionals to understand color perception, including the basic physiological details of how humans experience and understand color. We’ve highlighted some of them here, but there are many other, more detailed resources online. And a working knowledge the various methods of color measurement is also important, since these concepts are central to how light is characterized, quantified, and specified. CRI, CCT, and many more—these acronyms are part of the specialized vernacular of the lighting industry.

Color preference

Researchers have been exploring color preference to identify why people tend to prefer certain lighting sources and colors. As it turns out, many people tend to prefer lighting sources that had a larger gamut in the red area, causing slight oversaturation in the red range vs. daylight. Does this mean that lighting designers should specify more red? Ultimately, that’s a personal decision, one that weighs inherently subjective color preferences vs. staying realistic (e.g., close to daylight)—without distorting any individual color rendering.

 

 

Understanding the foundation

It’s helpful for today’s lighting professionals to understand color perception, including the basic physiological details of how humans experience and understand color. We’ve highlighted some of them here, but there are many other, more detailed resources online. And a working knowledge the various methods of color measurement is also important, since these concepts are central to how light is characterized, quantified, and specified. CRI, CCT, and many more—these acronyms are part of the specialized vernacular of the lighting industry.

How is color measured?

When the world was lit only by the sun, there was no real need to measure or quantify color. Light was simply light and colors were perceived by the world in a similar manner, though with the inherent variations created by perception and preference. With the advent of electric light sources (from incandescent to fluorescent to LED) came the need to quantify and accurately measure that light output1 —and to compare different light sources.

Here are just some of the ways that light is measured via scientific quantification:

Lumen output: A traditional form of measurement

The specification most commonly used for evaluating and comparing the performance of conventional lighting is lumen output. However, complete and accurate definitions of lumens and related terms are often technical and complex—and misunderstood. Lumen measurements should not be the only measurement considered when comparing light sources.

Correlated Color Temperature (CCT): A fundamental representation of white light

The CIE2 1960 color space shows a range of color temperatures, measured in degrees K (Kelvin) along the black-body curve, from red to orange to yellow to white to blue. This progression is similar to the way a piece of iron changes color when heated in a blacksmith’s forge.3

CCT provides a basis for identifying the quality of light by assigning a color temperature to that light. This approach works well with incandescent bulbs, which use a filament that is heated until it emits light—so the temperature of the filament is also the color temperature of the light. However, CCT doesn’t take into account human biology and perception of light. It simply compares the color of heated tungsten to the color appearance of a light source—making it functionally obsolete in an LED context.


Color-Rendering Index (CRI): How well a light source renders colors

Another key traditional measure of light and color is the color rendering index (again, devised by CIE), which measures the ability of a light source to reproduce the colors of standardized color samples—designated R1 to R8, with R9 (a saturated deep red color) often added. The color rendering score rates the faithfulness to the reference source—with a CRI of 100 being the highest fidelity compared to the reference source. For example, incandescent light sources have a CRI rating of 100. And color rendering under sunlight changes based on the time of day and weather conditions.

As with other traditional color measurement methods, CRI presents problematic issues when characterizing LED sources. For example, CRI cannot effectively predict the color quality of white-light LEDs. And different sources with the same CRI value render colors very differently.


For example, consider spectral power distribution. The three curves show wavelength content of three types of light—LED, fluorescent, and incandescent. While all three types of light create the same hue of white on a white wall, colored objects will render quite differently under each. CRI attempts to quantify source color rendering differences.


  1. Light output is the informal term for how much light a luminaire produces. The more technical term for data describing the visible light produced by a light source is photometrics.
  2. International Commission of Illumination, known as the CIE from its French title, the Commission Internatonale de I’Eclairage, an organization “devoted to worldwide cooperation and exchange of information on all matters relating to the science and art of light and lighting, color and vision, and image technology.”
  3. In fact, the black body is a theoretical object that absorbs all electromagnetic radiation that falls on it. Because it reflects no light, it appears black. And though no perfect black bodies exist, certain metals offer approximations.

 

Understanding the foundation

It’s helpful for today’s lighting professionals to understand color perception, including the basic physiological details of how humans experience and understand color. We’ve highlighted some of them here, but there are many other, more detailed resources online. And a working knowledge the various methods of color measurement is also important, since these concepts are central to how light is characterized, quantified, and specified. CRI, CCT, and many more—these acronyms are part of the specialized vernacular of the lighting industry.

Color Science in the LED Era

Traditional color science created a rational way for lighting designers and other to quantify the light output and describe specific color qualities of conventional incandescent lighting sources. CCT, CRI, and other measurements served as an accurate paradigm for defining light within that context. But as we’ve seen, the old standards are not ideal for the LED world. The accepted standards and their associated terminology will not go away (at least immediately) but will be supplemented by other, more precise ways of quantifying color—and differentiating between different light sources.

As it often does, digital disruption (LED lighting) has inspired a parallel effort toward standardization. At some point in the future, our industry will adopt a standardized way of evaluating light source color rendition. Groundbreaking efforts, including Color Quality Scale (CQS), Gamut Area Index (GAI)—and now IES’s TM-30—can be seen as important steps toward the goal of standardization. But the day-to-day reality for today’s lighting professionals is that they have many alternatives available when choosing how to achieve their creative vision. Knowing these alternatives—and their particular strengths—is critical.

Lighting design is all about choices.

For lighting designers, the initial choice is between the three main varieties of light—white, color, or color-changing effects. This choice then leads to a second level of decisions—what type of light source to use to create that light. Before choosing a specific luminaire, form factor, or vendor, lighting professionals face a core decision about what type of light source will work best for their application.

RGB, and beyond

For want of a better word, there are multiple approaches to color available now—which, ultimately, is good news for lighting professionals, who can tailor their choice to the specific needs of an application. In the past, designers had to use what was available, which meant RGB luminaires. But new options also trigger the need for careful decision making—backed by an understanding of the options.

Options from Philips Color Kinetics include:

RGB

RGB luminaires were the prevailing standard in color-changing installations for many years. Now luminaires combining red, green, and blue LEDs remain an option that allows a workable three-channel approach to creating color for a defined range of applications. It remains the default option for many luminaires, and gives lighting professionals a simple way to match legacy implementations—allowing for incremental addition vs. replacing all of the current luminaires.

RGB Chart

 

RGBA

Luminaires with red, green, blue, and amber LEDs expand the available range of colors to include warmer tones such as rich gold, yellow, and orange shades. The fourth channel enables creation of amber, a color that is impossible to achieve via color mixing of RGB channels alone. Whites will appear as the same color on a white surface, no matter what colors created it. But when viewing colored objects under the source, the differences become clear.

RGBA Chart

 

RGBW

Adding a separate white LED creates better-quality whites compared to RGB, but lacks the ability to make amber tones. It also enables saturated reds, and a full range of pastels—as well as creation of white and diverse color light in the same luminaire.

RGBW Chart

 

IntelliHue

Our advanced approach to color control and mixing produces an enhanced spectrum of precisely controllable light, including millions of saturated colors, pastels, and precisely controllable, high-quality white and tinted white light. By combining carefully selected channels of LED light sources, IntelliHue enables high-quality dynamic color and white light from the same luminaire.

IntelliHue Chart

 

These approaches give lighting specifiers options that can match the specific demands of their application—and achieve their creative visions.


Turning Science
into
Reality

How to choose the right type of luminaire to achieve
your creative vision

The expanding range of assignments and implementations now possible with LED lighting creates challenges and opportunities to today’s lighting professionals. What type of lighting is right for a specific job? Will it meet the expectations for color, brightness, and consistency?

Here are just a few real-world scenarios—indoor and outdoor—and our recommendations for the suggested type of Philips Color Kinetics luminaire.

Consistency
in the LED era

Much of LED color science focuses on bringing consistency to LED lighting. Without consistency, lighting professionals cannot rely on the quality and specific output of the luminaires they select. And larger implementations can show variations between luminaires. To address these needs, Philips Color Kinetics has developed key lighting technologies that set new standards for consistency. These technologies work together to deliver the ever-escalating levels of accuracy, precision, and consistency required by innovative tuned white, color, and dynamic color applications.

 

Optibin

Meticulous LED selection for maximum consistency

Optibin begins the color consistency process by grouping (or binning) LEDs by flux as well as CCT for white and center wavelength for color LEDs. This proprietary binning optimization process uses an advanced bin selection formula that exceeds industry standards for chromaticity to ensure uniformity and consistency of hue and color temperature for Philips lighting products.

Download the Optibin Technical Overview PDF. >>

Chromasync

Color precision and consistency

Chromasync provides advanced color consistency for dynamic color LED lighting applications. Chromasync is available on all Philips Color Kinetics IntelliHue LED Lighting Systems (and some RGB, RGBW, and RGBA luminaires), enabling them to achieve color consistency. Chromasync’s integration into Philips Color Kinetics LED lighting systems is ongoing.

Download the Chromasync Technical Overview PDF. >>

IntelliHue

Advanced color control and mixing

This advanced approach to color control and mixing that produces an enhanced spectrum of precisely controllable light, including millions of saturated colors, pastels, and precisely controllable, high-quality white and tinted white light. By combining carefully selected channels of LED light sources, IntelliHue enables high-quality dynamic color and white light from the same luminaire.

Download the IntelliHue Technical Overview PDF. >>

Staying at the forefront of an evolving industry

Lighting has evolved extensively in the last decade, thanks to the advent and advancement of LED technology. And there’s more change ahead as new solutions hit the market, and lighting professionals continue to explore the art and science of their profession. New options. New opportunities.

New ways to make an impact, indoors and outdoors. And even more in the future.

Knowing the core color science behind lighting is an ongoing effort, and one that Philips Color Kinetics is glad to share with our many customers throughout the world.

 

Color Matters

A Practical Guide
to Color Science
in an LED

Download the
Color Science PDF »

Color Matters Book