There are many reasons that LED solid-state lamps are becoming more popular for illumination. The obvious reasons for consumers include things like energy efficiency, and extremely long life. But for the design world LED has even more compelling implications. LEDs are cool to the touch and can be very small, allowing for integration into tiny spaces where incandescent and fluorescent lamps can’t go. LEDs also do not emit ultraviolet or infrared radiation and therefore do not fade fabric, accelerate the deterioration of papers or attract insects. As LED technology advances, it is the potential to precisely control color temperature and color rendering to invoke emotion in design that is exciting in terms of the way that light interacts with surfaces. Early specification of LED illumination was limited by the logistics of the power source, the availability of only bright, cool colors and cost. This basic overview of LED technology will explore why these reasons may no longer be relevant to specifiers, and why there has never been a better opportunity for LED lighting integration into furniture, cabinetry and millwork.

Rather than burning a filament, like an incandescent lamp, or exciting a gas, like a fluorescent lamp, LED lamps uses semi-conductors to create electroluminescence, a phenomenon first discovered by the British scientist H.J. Round in 1907. By the 1960s the first practical applications of visible-spectrum LED were developed and implemented into calculators. Soon LEDs were used for indicator lights as well as in a wide variety of appliances including: watches, telephone, radios and televisions. Since the 1960s LED technology has developed, in conjunction with semiconductor and nano-technologies, at an astounding rate; doubling in efficiency and light output every 36 months or so. It is no wonder that LED is furiously gaining ground in illumination applications.

HOW LED WORKS

Disclaimer: The following description is rather techie. If eye glazing-over occurs, skip to the next paragraph.

The diode in light emitting diode is a simple semiconductor device. Conventional LEDs are made from a variety of inorganic semiconductor materials. In its pure form, all the atoms of the semiconductor bond with their neighbors leaving no free electrons to conduct electrical current. The balance can be changed by either adding free electrons (N-type material, cathode) or by creating holes where electrons can go (P-type material, anode). This process of adding impurities, called “doping,” makes the material more conductive. Diodes are made with a section of N-type material bonded to a section of P-type material, creating a p-n junction. The inherent polarity of the diode is the reason that only direct current sources can be used for LED lamps. When an LED is switched on electrons are excited, moving from the P-type material across the p-n junction to the N-type material within the LED device. When an electron meets a hole it falls into a lower energy level releasing energy in the form of photons, a phenomenon known as electroluminescence. The energy gap of the specific semiconductor materials determines the color of the light.

From the above description there are two important things for specifiers to know. 1. LED lamps require a direct current (DC) power source. 2. LEDs are near-monochromatic light sources. They emit various colors (except white) depending on the materials from which they are made. Virtually any color and temperature can be achieved with LED, with three-channel red, blue green chips being the common output. For simplicity’s sake, red, blue and green are often used together to achieve other colors. Ultra-violet LED is used in combination with colored device chips to create white light.

POWER SOURCE: THE DRIVER

Electricity in practical applications can be thought of in terms of direction (current) and electrical potential (voltage). Most buildings are equipped with alternating current (AC) at different voltage capacities depending on usage and geography. LEDs require low voltage DC power. This requirement of low voltage contributes to LEDs energy efficiency, but it also poses a practical challenge. To utilize LED lamps in conventional spaces AC line voltage must be converted via a driver to a well-regulated lower voltage DC. The quality and consistency of the LED illumination depends both on the semi-conductor and the power source.

For general screw-in “bulbs” or lamps that are designed to fit standard fixtures, the driver is usually incorporated into the top hat. But in the design world, one of the really appealing characteristics of LED is the potential for integrating small lights into furniture, cabinetry and retail fixtures. This requires an outside driver, and historically a separate switch box. In most situations an electrician was needed to set up a system of LED lamps incorporated into furniture or fixtures. But like all other aspects of LED technology, drivers are becoming more refined. “Many people come out with what the customer sees, which is the light,“ says Philip Martin, who works in International Project Marketing for Hafele, “but not how it is installed by the factory or woodworker, or even designer. Hafele has developed a technology with everything needed for LED furniture and cabinet lighting into a universal plug and play system.” Hafele’s drivers, called Loox, come in two operating systems.

The constant voltage system is used with LED parallel circuits, providing a regulated voltage regardless of the current drawn by the load. “A common problem is using the wrong voltage driver,” says Martin. “When that happens the LEDs either won’t light up or could operate at a higher current then they are made for, reducing the lifespan of the lamps.” This system is normally used to drive low-to-normal power LED (12V and 24V) lamps.

The constant current driver provides a regulated current supply that allows the output voltage to adjust. It is typically used to drive high power lamps, and integrated resistors are unnecessary. “A constant DC current is necessary for optimal light output from the LED lamp without overstressing it,” says Martin. Hafele has also developed a series of switches that can be used with the system that allow for dimming, or to turn the system on with motion sensing or opening a door/drawer.

There are many specialized drivers available on the market, and while Hafele’s Loox system is designed to make it simple to integrate LED into furniture and cabinetry, not all drivers can be safely used by laypersons. It is always wise to check the voltage rating on the LED load being used against the rated voltage output on the driver.

PSYCHOLOGY OF LIGHT

Resistance to LED lamps is also because of the perceived quality of the illumination. Many people think LED and think bright, blinding blue light. Considering that light has a major impact on human well-being, from the healing process to the circadian rhythm that regulates biological and physiological functions, it is no wonder that quality of light is a big concern. “Blue light, for example can be soothing. But if the color temperature is high it is stimulating and causes wakefulness,” says Mark Smith, Senior Design Manager for Schattdecor. “Likewise it can be used therapeutically for people who are tired.”

While bright and cool may have been the initial offering to the consumer market, advances in LED technology have made it possible to acquire LED lamps in virtually any temperature and color. More about how this related to surface design in the next section. But first, it is helpful to know how the qualities of light are measured.

QUALITIES OF LIGHT

Basic color temperature is conventionally measured in the unit of absolute temperature by the Kelvin (K), scale, which is typically depicted as a vertical scale from 1K -7500K, Higher K values are cooler, and lower K values are warmer. But according to Lucifer Lighting Company, to precisely describe the color temperature of any light source it is important to consider both the spectrum and intensity of the light, a two-dimensional measurement described as the correlated color temperature (CCT). Here’s how it works.

The spectrum of visible light is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is what we call light. But with each wavelength there is also intensity, or the amount of light emitted at a particular wavelength. When the intensity of light from an object is plotted at each wavelength of visible light the shape is a smooth curve called the black body curve. The black body curve is a conceptualized physical body that absorbs all incident electromagnetic radiation. True color temperature is not a clearly defined point, but rather a slope that represents the intersection of the color temperature slope and the black body slope. Different lamp manufacturers have developed LEDs for a variety of applications ranging from 2000K (very warm, standard incandescent light is around 2700K) up to 10,000 K for industrial applications (so bright it exceeds the spectrum of visible light). The higher the CCT, the greater the efficacy of the lamp.

NOT ALL LEDS ARE CREATED EQUAL

Another means for describing lighting is the Color Rendering Index (CRI), which measures the ability of a light source to reproduce color faithfully in comparison with an ideal light source. The scale is from 1- 100, with daylight rendering 93 and typical values for artificial light falling between 60 and 80. When it comes to LED technology, the CRI of the lamp depends on the quality of the lamp. Lower quality LEDs have lower CRI and higher variability, where better quality LEDs have higher, more consistent CRI. This is important to designers considering incorporating LED lamps into furniture, fixture and cabinets as the lamp itself can have a significant effect on the surface design. “The issue of light pertaining to décor paper is metamerism,” says Peter Stasiowski, Director of Communications for Interprint USA. “We very carefully engineer our product to have consistent visual impact regardless of the lighting of the application or the texture imparted in the finished product.” But despite the vigilance of the décor paper printers, lamps that have a broad range of CRI or that fade quickly with fluctuating CCT can undermine the desired effect of a design.

High-quality LED lamps can be tiny in size and consistently specified for precise color and temperature, providing designers with the opportunity to play with integrated lighting in unprecedented ways. Advances in driver technology make application easy. And while up front cost for LED lamps is still an issue, the fact that a typical diode operates for 50,000 hours and uses 90 percent less energy than incandescent lamps and 40 percent less than compact fluorescent lamps (incandescents last 1,200 hours, CFLs 8,000 hours) the lifetime cost of maintenance savings, in terms of energy use and bulb replacement, make a compelling case for LED.