Tools for Comparison
For PAR lamps used in accent lighting applications, the principal metric used to measure output is often not lumens but center-beam candlepower (CBCP), a gauge of maximum luminous intensity, expressed in candela, at the center of the beam. A related unit of measurement is beam angle—the angle at which the luminous intensity measures half of CBCP. Beam angle determines whether the given lamp has a narrow, medium, or wide distribution. Among PAR lamps, typical beam spreads—the distance from one beam angle to the beam angle on the other side of the lamp—include narrow spot (9 to 10 degrees), narrow flood (25 to 30 degrees), and wide flood (40 degrees). Some lamps are available with a very wide flood (45 degrees-plus) emission. A PAR spot and a PAR flood may have the same light, but the spot will have a much higher center-beam candlepower luminous intensity.
Additional metrics, if available, include field angle and spill. Field angle, or cutoff angle, is the angle at which intensity measures 10 percent of total CBCP, and spill represents where emission outside the field angle fades to zero percent of CBCP. These tell us how well the lamp controls the beam pattern. Two lamps, for example, might have similar CBCP and beam angles, but the first lamp may have a smaller field angle and close spill, which means it offers a tighter beam (a harder edge) than the second lamp. Suppose a designer needs to light an object in front of a color backdrop. If the goal is to light the object only, he or she may choose the first lamp; if the goal is to light both the object and some of its surroundings, he or she may choose the second.
In addition to luminous intensity, beam spread, and optical control, other criteria to consider when selecting a directional lamp include color output and rendering, lumen maintenance, modeling, ease of dimming, energy and maintenance costs, and initial cost.
Ceramic Metal Halide
CMH lamps come in several choices: MR16, PAR20, PAR30LN, and PAR38 configurations. PAR30LN versions are available in 20W to 70W, and PAR38 versions are available in 22W to 150W, including 23W and 24W self-ballasted products in a range of beam spreads.
The ability of CMH lamps to deliver a brilliant, concentrated beam of light makes them well-suited to accent and tracklighting, in which they can replace incandescent spots on a one-to-one basis for a 50 to 70 percent energy savings. CMHs can also reduce the number of units needed by leveraging their ability to deliver two to three times more light for the same energy level. One 70W metal halide trackhead, for example, is claimed by manufacturers to be able to replace up to three 90W incandescent trackheads, resulting in a cleaner appearance.
While the color temperature of these CMH lamps is a little cooler than halogen (3000K to 4000K, compared to 2900K or lower), the lamps do have good color rendering (80 to 94), minimal lamp-to-lamp color variations, and stable color throughout their lives. To ensure good, ongoing color quality, group relamping is recommended. As a point source, CMH delivers good modeling, sparkle, and depth. These lamps are rated at 9,000 to 15,000 hours (at 10-plus hours per start, with lamp life being an average expected for a large population of lamps) compared to typically 3,000 to 4,200 for the most efficient IR halogen lamps.
CMH does not turn on instantly, however, requiring a warm-up of two to four minutes and restrike of four to six minutes, depending on the product. Also, consider its center-beam candlepower (CBCP) carefully to avoid substitutions that are overly bright for the application. CMH lamps require a ballast, which may be integrated or mounted separately.
Note that most CMH systems are not dimmable, so dimming of the track will severely shorten lamp life in tracklighting applications. Lumen maintenance at end of life can be as low as 60 percent or less. Finally, CMH lamps tend to produce some spill light, so they are best suited to applications where you want to light not just an object, but also its surroundings. When choosing CMH for a retail application, be sure that the product has a satisfactory R9 CRI to ensure good rendering of saturated reds.
LEDs
This technology is ideally suited to directional lighting applications because the light source is inherently directional, resulting in very high efficiency. Additionally, the general form of the directional lamp allows ample heat sinking (which may or may not be aesthetically desirable for tracklighting, depending on the project). The most recent series of reports from the DOE’s CALiPER testing has demonstrated that LED PAR30 and PAR38 lamps can be more efficacious than IR halogen while providing similar performance, resulting in 70 to 80 percent savings in energy use.
Several LED options are available in AR111, MR11, and MR16; R12, R16, R20, and R30; BR and ER; and PAR16, PAR20, PAR30, PAR30LN, PAR36, and PAR38 configurations.
A wide variety of lumen output levels and beam angles is available with directional LEDs, offering greater flexibility than conventional products. These lamps offer excellent beam control, and typically render saturated colors well. Lamps are available in a variety of color temperatures from 2700K to 6500K, and some luminaires are available with color tuning.
LED directional lamps have additional benefits, including long-rated service life (typically with no spot-relamping needed for years) of 25,000 to 50,000 hours; a failure mode based on lumen depreciation (L70) instead of outages; no radiated heat and ultraviolet output (will not cause colors to fade over time); and no mercury content. Some products are available with a black or white finish at the back of the lamp for heat sinking, which results in an integrated trackhead appearance.
While LEDs are a good option for directional lamp replacements, it is important to note that LEDs are still a young technology. The quality of the light may not produce the same texturing effects as halogen, and LED cannot match CMH and IR halogen at the high end of the range of light output and luminous intensity. Not all LED products are dimmable, and those that are may not be compatible with selected controls.
Some LED products have low CRI ratings, but are good at rendering the saturated colors typically found in retail—pastel colors are used in the standard CRI test. A new color metric, the Color Quality Scale, is being vetted by the lighting industry as an alternative to CRI. This scale takes into account the color-rendering characteristics of white-light LEDs better than does the CRI scale. (See “After CRI,” Jan/Feb 2012.)
This is a get-what-you-pay-for time in LED technology. High-performing products come with a significant initial cost; low-end products may exhibit flicker, color distortion over time, and other performance issues. Some products have lamp dimensions—diameter, maximum overall length, neck geometries—that do not meet the ANSI-defined formats of the lamps they are supposed to replace. (Even if they do, they may not fit the same luminaires as a given halogen lamp; it’s best to check.) Note that the lamp’s performance warranty may include limitations on the daily number of operating hours. Also, product performance may vary significantly from manufacturer to manufacturer, and equivalency claims may be exaggerated or misleading.
There are benefits to requesting samples of LED products and producing mock-ups prior to making final decisions. Doing this gives the designer the opportunity to see the quality of the light, including its texturing, brightness, and color effects, while verifying compatibility with controls, space constraints, aesthetic needs, and so on. Designers can also reduce risk by looking for products that are properly tested to industry standards such as LM79 and LM80, and those that carry the Energy Star quality mark, which provides assurance that the product performs similarly to the product it is intended to replace, but using less energy. Specify lamps listed to UL standards, and consider specifying lamps that have performance warranties that cover lumen maintenance and color shift over time.
This July, regulations will make higher-end options such as LEDs more economically attractive. Ultimately, the right choice for a halogen replacement will depend first on the lighting needs of the application—beam spread and control, color quality, dimmability—and then on the economic factors involved, such as energy, maintenance, and first costs.