ARTIFICIAL LIGHTING AND COLOR

Depending on the type and age of a building, you may encounter a range of artificial lighting systems, from incandescent and halogen to fluorescent and LEDs. Often buildings will include a combination of lighting types and will supplement artificial lighting with daylighting.

You likely understand intuitively that certain colors look more appealing when illuminated by certain types of artificial lighting compared to others. These differences can largely be explained by the differences in color temperature, color rendering index, and efficacy (efficiency) of these light sources. Understanding these characteristics can help design professionals select the ideal paint color for both residential and commercial projects. It can also help designers take into account how artificial lighting systems and color impact occupants’ well-being and productivity.

Photo courtesy of Benjamin Moore & Co.

Incandescent Lighting

The incandescent, or Edison bulb, has been with us for over 100 years, with the basic technology unchanged. These lamps produce light via a tungsten wire filament that is placed inside a glass bulb. When an electric current is passed through the filament, resistance in the filament creates heat, and the bulb glows. As we saw earlier, the spectral power distribution graph for incandescent lighting shows that there is much more energy toward the red end of the spectrum, which explains why incandescent bulbs produce such warm light.

Incandescent lighting has a CCT of about 2700 K and its CRI is 100, meaning incandescent lamps are very good at rendering color. Unfortunately, these lamps are highly inefficient. About 90 percent of the energy is lost as heat, and their life expectancy is short. Consequently, incandescent lamps are being rapidly phased out in the name of energy efficiency. The United States has set efficiency standards that, in effect, preclude the manufacture or importation of certain incandescent lamps. As of this writing, a second tier of even more stringent standards has been delayed.

LED TECHNOLOGY

First introduced in the 1960s, light-emitting diodes, or LEDs, use solid state technology (SST) to emit light. For these lamps, a semiconductor chip is embedded in plastic. When voltage energizes the chip, the movement of electrons generates visible light. Different semiconductors release different wavelengths of light, and this determines the color of the light produced. Diffusers and other elements can be used to focus or scatter the light. LEDs run on direct current and usually include a built-in transformer in the power supply.

Unlike other light sources, LEDs don’t emit heat as infrared radiation. All of the heat is internal, but it must be removed by conduction in order to maintain light output, life, and color. Thus, all LEDs include a heat sink, which is a key component in a high-quality LED.

LEDs only produce light of a certain wavelength, or color. There is no such thing as a “white” LED; instead, the light from LEDs is mixed or manipulated to produce white using two main methods.

In the phosphor method, blue diodes are coated with a yellow phosphor. When the photons emitted by the diode travel through the phosphor layer, they either pass through or are converted into photons of a different wavelength. This combination creates light that appears white. The color temperature is determined by the dominant wavelength of the blue LED and the composition and thickness of the phosphor layer. Yellow phosphor LEDs tend to create bluish-white light and have CRIs in the range of 75.

Researchers have been developing new phosphors that enable warmer white light, and some LEDs include two or more types of phosphors to better represent the spectrum of visible wavelengths. In particular, red phosphors help fill out the red wavelengths, as single-phosphor LEDs are usually deficient in these tones. LEDs created through the phosphor method are very efficient and are capable of CRIs of 80 or more, although red phosphors lose some energy in the form of infrared wavelengths.

In the “RGB method,” white light is created additively by varying the intensities of individual red, green, and blue LEDs. This method allows precise control over the color of the white light; however, it requires more hardware since a lamp must include three LEDs. Also, these lamps tend to render pastel colors poorly.

Some LEDs utilize a hybrid of the phosphor and RGB methods.

Halogen Lighting

First patented by General Electric in 1959, halogen lighting is considered a type of incandescent lighting, but with several advantages over the Edison bulb.

Halogen lighting is about 20 percent more efficient than conventional incandescents. More energy is released as light, and the lamps have a longer service life. The bulbs burn at a continuous level of brightness and have a life span of about 2,000-3,000 hours.

The spectral power distribution of halogen lamps is the closest of all light sources to daylight; it’s relatively balanced across the visible spectrum. Consequently, halogen is considered an ideal light source.

The color temperature of halogen is approximately 3000K, which is considered “warm” light, and it renders color at 100 percent. This relatively high color temperature enables good color rendition across a wide range of colors.

On the downside, halogen lamps have a high operating temperature, and while they are more efficient than other incandescents, they are far less efficient than LEDs. Hence, many countries have begun phasing them out, and in the United States they are rapidly being replaced by LEDs. Also, the light quality is not consistent. Though bright and white at maximum output, when dimmed, halogen light appears amber.

In addition to specific applications in homes and commercial buildings, such as task lighting, halogen lamps are also used for film projectors, vehicle headlights, floodlights, work lights, and in film production.

LEDS GET SMART

Advances in LED lighting technology are enabling lights in a wide range of color temperatures and with better color rendering. Some manufacturers also offer products that allow users to select and change color temperature of the same bulb. This might be desirable to help set a certain mood or promote a certain type of activity. For instance, light in the blue portions of the spectrum promotes wakefulness. Consequently, a cooler, brighter white LED—one that is closer to bright daylight—can help people focus and perform tasks, while warmer light may help promote calm and prepare us for sleep at the end of the day. In fact, increased interest in “human-centric” lighting has led to the development of tuneable LEDs—those that mimic the condition of daylight from morning to night. Some of these products can be programmed and/or controlled remotely using a smartphone or even voice control.

Fluorescent lighting

Though the technology was developed in the 1880s, the first fluorescent lamps weren’t available commercially until the 1930s. These lamps work by exciting a vapor inside a glass tube. As electricity passes between tungsten cathodes, the mercury vapor releases ultraviolet energy. A phosphor coating on the inside of the tube converts the UV light into visible light—a process called fluorescence.

Fluorescent lamps require a ballast, which controls the current to the lamp. The current must be modulated as the gas inside the tube ionizes and the resistance lowers; otherwise, the lamp would destroy itself.

From classrooms to grocery stores, fluorescent lighting is widespread in commercial and institutional buildings. Fluorescent lighting is seen in residential settings, particularly kitchens, and compact fluorescent bulbs, or CFLs, have replaced the traditional Edison bulb in many homes.

The light produced by early fluorescent lamps was cold and undesirable; however, phosphor technology has improved, resulting in more pleasing light with higher CRIs.

The spectral power distribution graph for fluorescent lighting reveals spikes at the red, green, and blue wavelengths, with little or no output at others. Colors appear cool. Blues and greens are enhanced, while reds and yellows are muted.

Fluorescents are available in a range of color temperatures, from warm whites (2700 K) to cool white (6500 K), and they have CRIs in the 80-plus range. They have a life span of about 8,000-10,000 hours.

There are several types of fluorescent lamps. Linear, or tube lights, remain popular for their energy efficiency and their even, diffuse lighting.

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Originally published in June 2022

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