away from the incandescent lamp to more energy efficient alternatives such as CFLs and solid-state options (LEDs and OLEDs), the basic terms used for lighting discussions also need to change. Instead of thinking in terms of watts, consumers now need to learn a different measurement system, one that tells them how much light a product is going to emit (in absolute terms or per unit of power consumed) instead of the rate at which energy will be consumed. And this is just the beginning of the changes that consumers are likely to see if LED and OLED lighting continue to improve at their current rates. In this section, several key concepts and terms used in the lighting industry are introduced that will be used throughout the rest of the report.
Lighting designers and engineers use different terms for lighting equipment than are used in the vernacular. In this report, the engineering terms will be used. A luminaire is the combination of light fixture hardware, a ballast or driver if applicable, and a light source, commonly called a lamp (i.e., a light bulb). Thus, the term lamp can refer to an incandescent bulb, a CFL bulb, or an LED replacement “bulb.” This report will use the term lamp. A luminaire consists of, minimally, a lamp holder, commonly called a socket, and the way to connect the socket to the electrical supply. Most fixtures also contain optical elements that distribute the light as desired, such as a reflector, lens, shade, or globe. When needed, fixtures and luminaires contain a ballast or a driver. A ballast is an electronic device that converts incoming electricity to the proper voltage and current required to start and maintain the operation of a lamp. The term driver refers to the corresponding device used in an SSL luminaire. Luminaire examples include chandeliers, downlights, table lamps, wall sconces, recessed or pendant mounted luminaires, and exterior streetlights. When equipped with lamps, they are called luminaires. The types of lamps typically encountered are discussed below in the section “Annex.”
The portion of the electromagnetic spectrum that can be perceived by the human visual system is called the visible spectrum. The amount of light, weighted by the sensitivity of the visual system, emitted by a source per unit time is its luminous flux (Figure 1.3) and is measured in lumens (lm). This makes lumens one of the appropriate pieces of information for lamp packaging to help consumers choose the appropriate replacement lamps. Lumens provide a description most closely related to brightness and should be referred to when choosing replacement lamps. A proliferation of fact sheets and labels has accompanied the recent introduction of new lighting technologies, leaving some consumers confused about the relationship between watts and lumens. That relationship is determined by the energy efficiency of the product. Watts describe the amount of electrical power consumed by the product, and lumens describe the rate at which it emits light. For example, most 60 W incandescent lamps emit approximately 850 lumens. Similarly, many 13 W CFLs emit 850 lumens.
FIGURE 1.3 Luminous flux (lumena).
FIGURE 1.4 Luminous intensity (candela).
Luminous intensity (Figure 1.4) is the luminous flux per unit solid angle, evaluated in terms of a standardized visual response and expressed in candela. The magnitude of luminous intensity results from luminous flux being redirected by a reflector or magnified by a lens.4 This measurement is used primarily to describe the specific light intensity and
4 The concept of solid angle has a strict geometric definition but can be thought of as a way to describe the focusing and redirecting of a light source by the lenses and reflectors in the luminaire.