White Light Color Tuning Offers a New Dimension of Lighting Control

Light is comprised of wavelengths that the human eye interprets as colors. For an object to be perceived a certain color, that color must be present both in the light striking an object and the object reflecting the light towards the observer’s eye. Because of this, the choice of lamp for white-light general lighting can influence how colors are perceived in a space. This means that perception of objects in the space is, to an extent, controllable.

 

Color temperature scale with approximate examples.

10000+K	North light (blue sky)
7000K	Overcast daylight
6500K	Daylight fluorescent lamp
6000K	Cloudy sky
5500K	Direct mid-summer sunlight
5000K	Direct sunlight, noon daylight
4500K	Sunlight in early morning or late afternoon
4000K	Clear metal halide lamp, cool white fluorescent
3500K	Neutral white fluorescent
3000K	Incandescent lamp, halogen lamp, warm white fluorescent
2500K	Sun at sunrise or sunset
2000K	Candle flame, high-pressure sodium lamp
1500K	Match flame

Traditionally, this level of control was extremely limited. To change the shade of white from warm (about <3000K) to neutral (about 3500K) to cool (about >4000K), we would essentially have three choices: 1) change the lamp, 2) add a color filter to a luminaire, or 3) separately control layers of warm and cool lamps. These options could be expensive and offered limited flexibility.

In contrast, solid-state lighting offers new possibilities for controlling color temperature. This would involve a master controller to control the system, DMX, DALI or other interface between the master controller and each LED product, and LED products with separately dimmable arrays of warm and cool LEDs or separately dimmable colors mixed with white. Depending on the LED product, it may 1) provide programmable and user color tuning, 2) imitate the warm color of incandescent lamps when dimmed, and/or 3) offer precise color matching between LED products and calibrate to maintain constant color output over their life.

Focusing on the first option, why should we care? The simple answer is the color qualities of a light source can affect the appearance of a space. In some applications, color is critical. In a high-end retail application, good color quality can make products, especially clothing, appear more vibrant, truer and ultimately more appealing. In an office application, color quality can facilitate social interaction by rendering faces more naturally and thereby helping to create a more productive and appealing work environment. In a healthcare application, good color choices can make guests feel more welcome by imitating the warm lighting conditions of home, while rendering skins more effective to help detect illness (jaundice, rash, infection, fever, etc.).

The list goes on. Think about the application: Do you want it to be visually warm or visually cool? The right color temperature is often a matter of psychology—both preference and tradition—with due consideration for emphasizing (and not distorting) dominant colors in the space and properly rendering color contrasts that make tasks more visible or call out safety markings and instructions.

When making a case for a light source, particularly as a retrofit option for an existing building, it’s highly beneficial to make an economic argument that goes beyond energy and maintenance savings. If the designer can effectively connect economic benefits to various aspects of lighting quality, the owner will be more amenable to paying more for these choices because they will perceive a return on investment. Color is one such area. As one small example, consider the results of three German experiments in which more than 500 people tasted white Riesling wines under different lighting conditions. The researchers used a series of fluorescent lamps that produced red, blue, green or white light. People rated the wine’s quality higher, in general, when they drank it in a room whose ambient lighting was red or blue versus green or white. They also found the test wine much sweeter and fruitier when sampled in a room lighted with fluorescent lamps with a warmer color tone, and were willing to spend more for it.

The problem is the right choice of color temperature is not always clear. The challenge becomes more significant in spaces that would benefit from different shades of white (and other colors) depending on different functions or times of day or year.

A survey of lighting designers and specifiers conducted by the National Lighting Product Information Program revealed that for retail applications, light source color properties are considered more important than any other light source criterion, including energy efficiency. Now imagine a light source that could be tuned—precisely, exactly where you want it—to optimize presentation of various merchandise displays. Color output could change based on time of day, as merchandise displays change, or fashion season. In change rooms, color output could be manually adjusted by customers to view themselves under different lighting conditions.

Now consider an office building where general lighting in daylighted spaces could automatically adjust to blend electric light with daylight, or where general lighting in non-daylighted spaces could automatically adjust to match the actual or idealized daylight cycle, providing visual cues about time of day. In meeting spaces, color output could be manually adjusted to adapt the space for different functions such as business meetings and social events.

Finally, imagine a hospitality space where color and décor are critical; the designer could tune the color output with the owner and other designers to achieve a precise space appearance after the final colors and materials are selected and the luminaires are installed. And later, at any time, to accommodate future changes. In a restaurant, color output could be adjusted from cool lighting during business luncheon events to warm lighting for evening dining.

Choice of color output with light sources is nothing new. The proliferation of solid-state lighting, however, is making that choice flexible and dynamic. The result is the ability to fine-tune the color quality of lighting for significant application benefit and intriguing possibilities awaiting exploration.