Lighting plays a critical role in retail spaces. It can attract customer attention; display merchandise in a compelling way; affect customer experience; and communicate brand, quality and price point.
However, a Pacific Gas & Electric and the California Lighting Technology Center survey of 87 retailers in 2012 found that a majority were unhappy with their lighting. Nearly 75 percent were considering upgrading to light-emitting diodes (LEDs), but more than half (54 percent) cited “lack of understanding” as a reservation. This provides an opportunity for electrical contractors to be educators about LED technology and good lighting practice. In this column, we explore the metrics used to evaluate the right reflector lamp (MR16, PAR30, etc.) for an application. Using this information, ECs can identify LED lamps that will provide performance that is equivalent to existing lamps and otherwise will best serve the application need.
It is useful to evaluate reflector lamps as input/output devices. The input is wattage. The output is light, measured in lumens. The resulting efficacy is expressed as lumens per watt. This is a good starting point for evaluating efficiency. But application efficiency is also important. Does the light go where we want it? If we want to highlight a display and end up throwing lumens all around it where we don’t need them, that’s a waste of energy.
To determine whether a product will put light only where we want it, several metrics become important. The first is center-beam candlepower (CBCP), measured in candela, which expresses the amount of light intensity at the center of the beam. Next is beam angle, measured in degrees, which indicates the beam pattern. The beam angle may be a very narrow, narrow spot, medium or wide-flood distribution, providing a choice of patterns and enabling users to light anything from a small object to a large display. How much light do you want to strike the object? How large is the object or area being illuminated, and how far away is it from the lamp?
That’s not all. The field angle and spill are within the beam angle. The field angle is the angle at which light intensity is 10 percent of the CBCP. Spill is the intensity of light falling outside of the field angle to the edge of the light beam. Field angle allows us to more precisely focus light on an object, while spill enables a choice of a very crisp or soft edge to the light pattern.
Field angle should be considered in lamp evaluation because two lamps with the same beam angle may produce different results. For example, suppose we want to highlight a tall, slim statue on a pedestal. We’re considering two lamps, one with a wider field angle and the other with a narrower field angle. If we want to focus the light beam to illuminate only the statue, the lamp with the narrower field angle may be preferable. If we also want to put a little light on the pedestal and surround, the lamp with the wider field angle might be the better choice. In this case, the lamp with the narrower field angle might produce fewer lumens, but we wouldn’t be sacrificing anything, because that lamp precisely illuminates what we want lit up.
Rated service life, expressed in operating hours, is important to retailers. Non-LED lamp life is expressed as an average, the point at which half of a large sample of lamps is expected to fail. LED lamp life is typically rated based on lumen depreciation over time, the point at which the average lamp is expected to produce a designated fraction of its initial light output, such as 70 percent (L70). Long service life affects maintenance costs, which can help justify investment in long-life lamps, such as LED lamps. However, retailers should be advised that LED lighting is not “maintenance-free” because lamps should still be re-aimed periodically to account for changes in displays over time.
Color appearance and rendering are two other important considerations. The color appearance of the light source and the light it emits is evaluated using color temperature, which may range from warm (orangish-white, around 2,800K) to neutral (3,500K) to cool (bluish-white, around 4,000K). The color rendering ability of the lamp, suggesting how natural colors look under its light, is expressed by its color rendering index (CRI) rating. For retail applications, a CRI of 90+ is often desirable, with a good R9 color reference rating to ensure good rendering of reds.
A final consideration is control. Lamps that will be dimmed must be designed and rated as dimmable and must be paired with a dimmer that is specifically rated as compatible.
As retailers transition from incandescent and halogen reflector lamps to more-efficient lamps, such as LEDs, they should be advised to look beyond watts and cost, and instead focus on products that will perform the best, put the right amount of light exactly where it is needed, and render merchandise in its best light. Because seeing is believing, it’s often recommended to show retailers a sample installation before commitment.