TOM JORY and JAMES ZHAI describe how LED-based lighting with spectral enhancement can replace legacy sources in demanding applications such as retail and hospitality.
Retail shops, with their long operating hours, have been among the earliest adopters of LED-based solid-state lighting (SSL) due to its high energy efficiency. Retail lighting is on anywhere from 12 to 24 hours per day, so the 80% improvement in energy efficiency for SSL pays off quickly. High-quality light and good lighting design are essential to attractive presentation of merchandise - and, therefore, to a store's success. Energy-efficient lighting is of no benefit to store owners if their merchandise appears dull and colorless. Retailers have thus helped to push the SSL industry to deliver higher quality of light with good color rendering and a broad range of color temperatures.
Store lighting design is also important for the retailer's brand image. SSL offers great flexibility in lighting design - from low ambient to high-flux spot illumination for driving attention to key product displays. Digital controls make high-contrast SSL easy to achieve. And since LED lighting produces no heat in the beam, very high flux levels can be poured onto high-value merchandise to draw customer focus without creating a hot, uncomfortable shopping experience.
Legacy lamps and narrow beams
One area, however, where retailers have been reluctant to move away from conventional lighting technology is in the use of ceramic-discharge metal-halide (CDM) or ceramic-metal-halide (CMH) lamps. They produce very high-quality light, have good light maintenance, and offer greater longevity relative to halogen lamps, which balances their relatively higher cost. Their greatest competitive advantage over high-quality SSL has been their ability to produce high flux density in a narrow beam or high center beam candle power (CBCP).
CDM lamps used in spot, track, and down lighting are central to the dramatic illumination needed for high-contrast lighting design, including the ability to illuminate a small area with high flux levels to attract customer attention to important merchandise displays. For example, CDM PAR30 lamps are generally offered in 35-39W and 70W power consumption variants. The CDM 39W PAR30 lamp has a spot beam spread of 10~15° with an initial lumen output of around 2400 lm. This lamp has a CBCP of 30,000~40,000 cd. CDM 70W PAR30 lamps have spot beam spreads of 10~15° with an initial lumen output of around 4800 lm and a CBCP of 40,000~60,000 cd.
FIG. 1. Directional LED-based lamps deliver focused lumens on the target.
Having met retailers' demand for both higher lumen output levels and higher quality of light, SSL source manufacturers are now challenged to reproduce in LED-based light sources the high narrow-beam flux density delivered by CDM lamps, described above. Achieving this goal will allow SSL to replace CDM lamps in track, spot, and down lights, as well as other key lighting applications. Luminus is one SSL source manufacturer working to address these important applications for retailers. From its earliest days, Luminus has gained experience working with very high-flux-density solid-state sources in high-drive-current packages for specialty lighting applications such as projection and entertainment lighting. The company has used this experience, combined with its chip-on-board (COB) light source technology for general lighting applications, to develop its high-lumen-density XH series light sources.
Comparison of candela on target between metal- halide PAR30 and fixtures with high-density COB light sources.
Products (9-mm-diameter COBs)
Initial lumen output (lm)
Initial candela on target with 10° beam
Initial candela on target with 25° beam
GE Constant Color 39W metal-halide PAR30L
30W PAR30L with CHM-9-30-80-36-XH00 (high-density COB)
Replacing CDM with COB LEDs
Such high-lumen-density COBs enable luminaire and solid-state lamp OEMs to drop a component into their existing spot, track, and down light luminaire designs or replacement lamps. These new light sources can deliver a shaped beam from 10° narrow spots for intense light to 25° narrow flood beam spread for accent and down lighting applications while still maintaining small form factors for luminaire OEM designs or PAR30 and PAR38 lamps.
The ultrahigh-density COB arrays can be provided in a range of standard light-emitting surface (LES) diameters such as 6, 9, 11, and 14 mm, which again simplifies the integration of these CDM replacement light sources into existing designs. SSL lamp and luminaire OEMs can use their existing ecosystems for optics and connectors, while delivering new bulbs and fixtures with higher lumen output and increased CBCP to their customers.
For example, the 9- and 11-mm XH series COBs are enabling fixture performance with the light quality and intensity to replace 39W and 70W metal halide sources, respectively. The table shows a performance comparison between a 30W PAR30L with CHM-9-30-80-36-XH00 and a GE Constant Color 39W metal halide PAR30 lamp. The small-form-factor 6-mm XH series at 3000K CCT generates 1500 lm and when combined with an 85-mm-diameter optic, throws an 8° beam with CBCP greater than 30,000 cd. These parameters can allow XH sources to serve as LED-based, high-wattage MR16/PAR lamp replacements.
FIG. 2. A PAR30 lamp design with an ultrathin hybrid reflective/refractive lens forms an efficient beam.
Solutions such as this allow retailers to have tight, narrow-beam spot lights that will deliver the punch needed to draw customers' eyes to targeted merchandise, as well as the high quality of light delivered by CDM lamps - but with SSL lamp and luminaire design flexibility and energy efficiency (Fig. 1). Plus, retail lighting can achieve much greater longevity with LED-based products than with CDM lamps - further reducing retailers' operating and maintenance costs.
Ultrathin hybrid lenses
It is important to have SSL lamps with the same PAR30 form factor of CDM lamps for easy drop-in replacement in the existing sockets for retail applications. An ultrathin hybrid lens is an enabling technology to solve the challenges of integrating SSL PAR lamps with sufficient heat-sink surface area for heat dissipation while still allowing enough room for the driver. Fig. 2 shows how an ultrathin hybrid lens enables adequate thermal dissipation surface area and fits the integrated driver as well as showing how a folded beam is formed through the hybrid reflective/refractive lens.
FIG. 3. The beam spread distribution of reference design 75-mm ultrathin hybrid lenses is depicted on the left at 10° and 16 cd/lm, and right at 25° and 4.2 cd/lm.
In a reference design optimized for high-density COB LEDs such as the XH series, a 75-mm diameter ultrathin hybrid lens with only 18-mm thickness can deliver a lens efficiency k-factor of 16 cd/lm for a ~10° beam, and a k-factor of 4.2 cd/lm for a ~25° beam from a 9-mm COB. Fig. 3 shows an example of hybrid lens beam profiles with 10° and 25° spreads.
Marrying color saturation and density
Another added benefit of this LED technology over incumbent CDM lamps is that retailers can take advantage of SSL's ability to offer a range of color qualities - including recently introduced, innovative below black-body line (BBL) and high gamut area index (GAI) light sources. Light sources using this technology are now offered by several manufacturers. Luminus, for instance, introduced this technology in 2014 in its Sensus product line. Fig. 4 shows Sensus product color points in a 1931 CIE diagram for 3000K and 3500K color temperatures.
Fig. 5 demonstrates how Sensus technology enlarges the Gamut area by delivering more saturated blue, green, and yellow. This lighting technology also delivers crisper whites and produces vivid, more saturated colors by moving the chromaticity on the CIE chart below the BBL, where the human eye perceives pure white. This movement, away from the traditional ANSI yellowish warm chromaticity, can create a lighting experience that customers perceive as brighter, with more vibrant, intense colors - a clear advantage for retailers (Fig. 6).
FIG. 4. The 3000K and 3500K Sensus LEDs hit the demonstrated spots on the CIE color diagram.
FIG. 5. The 3000K CRI-90 Sensus Color Gamut Area Index and color quality icon show more saturated blue, green, and yellow hues.
As these new light sources have entered retail applications, retail lighting manufacturers have increasingly asked for below-BBL light quality technology to be combined with a high-lumen-density COB configuration. The combined benefit allows retailers to use intense, narrow-beam illumination with a light quality that enhances the color saturation of the merchandise on display. "Our retail lighting design customers are really excited about the marriage of these two technologies," said Jack Lam, president of RIO Light. "Store lighting systems using these technologies allow retailers to effectively draw the attention of their customers to a particular merchandise display from across the store. Once the customer's interest has been captured and they've been drawn over to the display, retailers can present the products in a very pleasing light. The whiter whites and the brighter, more vivid colors really add to the appeal of the merchandise."
Flexibility in color quality
Phasing out the last CDM lamps offers retailers benefits beyond cost, quality of light, and flexible lighting design attributes. It allows them to simplify their entire operation, controlling light as never before. They won't need a mixture of lighting technologies, separate maintenance schedules for conventional and SSL technologies, or a replacement lamp inventory. As mentioned previously, lamp and luminaire manufactures can now change light source characteristics without redesigning their luminaires. It's a matter of dropping in a desired COB component - sharing the same form factor - but delivering a variety of color temperatures and qualities designed to enhance the customer experience.
FIG. 6. Retail lighting enhances the shopper experience with Sensus Color pure white.
With a total conversion to solid-state lighting, retailers can essentially future-proof their stores. They will now have enormous flexibility not only in selection of color quality and lighting design, but will also position themselves for adoption of new lighting control systems and integration with emerging Internet of Things (IoT) technologies. By transforming their shop lighting from an operational cost into a strategic asset, retailers can efficiently manage their business while providing a unique environment for displaying merchandise in a way that reinforces the store's brand image and creates a comfortable, inviting environment in which customers can browse and buy.
TOM JORY is vice president of illumination marketing and JAMES ZHAI is director of application engineering and technical business development at Luminus Devices (luminus.com).