September 1, 2001
by Ernest Wotton
Lighting plays a critical role in the design of successful retail environments, both in the creation of a comfortable atmosphere for shoppers and in the presentation and display of merchandise. A wide variety of options, each with its own particular strengths and weaknesses, are available for this demanding market. Of the lamp types discussed in this article, some are just being introduced to Canada, while others are still in development and will take some time to be widely available.
Choosing the right colour lamp
Nowadays, most lamps used in store lighting have good colour qualities. In the context of retail, colour is used as a sales tool. How should one choose from the wide selection of available lamps?
Among the data published by lamp manufacturers are two criteria affecting lamp colour qualities: Colour Temperature (CT) and the Colour Rendition Index (CRI). CT specifies the whiteness of a lamp; the lower the CT, the “warmer” the light. A typical fluorescent lamp used in store lighting may have a CT of 3000 to 4000 Kelvins (K).
Two lamps may have the same CT but the appearance of coloured objects under them may be different; this means that their colour rendering properties are different. The effect of light on coloured objects is known as colour rendering, and this has led to the development of the CRI.
The colour of an object as we perceive it depends on the colour rendering properties of the light hitting it. For example, a red car will not look the same under daylight as it does under a high pressure sodium lamp. The general colour rendering index is based on the shift in colour of eight samples when seen first under the light of a standard lamp, and then under the light from a lamp being tested for its colour rendering properties.
There is a consistent tendency for manufacturers to use the CRI as a figure of merit, but designers should be aware that this practice has limitations, and should observe several rules of thumb. Comparison of CRIs is meaningful only if it applies to lamps of the same CT. If the CRI is less than about 85 (the CRI of daylight is approximately 100), then the comparison between even lamps of the same CT is of questionable value. If the lamps have the same CT and the difference between CRIs of about 85 is no more than three or four, then it is very unlikely that observers will perceive any difference in the colour rendering properties of the lamps.
From experience as an expert witness, I have concluded that before people are given a responsibility involving the choice of colour, their eyesight should be tested to ensure that they have normal colour vision. Not doing so can lead to the selection of unwanted colours. This is not a rare or exceptional situation: about one man in 12 has some degree of colour blindness (as opposed to about one woman in 200). Colour vision changes with age, and the use of medication can also affect that vision.
LEDs: the light of the future?
A light emitting diode (LED) is a lamp that produces light when a direct current (DC) voltage is applied to a specially prepared semi-conductor material. The colour of the light depends on the material used.
LEDs are not new. For some 30 years, they have been used as indicator lights in digital watches, calculators and illuminated displays. But now, major lamp manufacturers are being persuaded of the possibilities for the use of LEDs as light sources in much the same way as many of the commonly used lamps included in their catalogues. Consequently, several manufacturers have formed joint ventures with semi-conductor specialists to develop LEDs. It may well be that Opto Semi-Conductors, LumiLed and GELcore will become as well known as Osram-Sylvania, Philips and GE Lighting, respectively.
LEDs are compact, produce a concentrated beam of light, and have a long life that could conceivably exceed that of the luminaires in which they are housed. At present, the main LED colours available are blue, green, red, yellow and amber. They have been used in displays, the LEDs being controlled by a microprocessor that mixes their light to produce almost any colour. So far, no naturally white LED is available; white LEDs are actually blue LEDs coated with a phosphor that emits white light.
There are several main thrusts in current LED development. One is aimed at improving the efficacy of the white lamp. It is anticipated that an efficacy of 50 lumens per watt, possibly more, will be achieved within five years. Another focus is to ensure that the colour of the light emitted by an LED is consistent, so that all lamps look the same. Also, research is being conducted to ensure that an LED appears to be the same colour regardless of the angle of view.
So far, only simple lighting devices incorporating LEDs and suitable for use in stores are available. They include a strip edge indicator and an MR16 size spotlight housing LEDs. It seems likely that in the near future standard LED devices will be restricted to those for store display lighting. The LED manufacturers are keeping their development programs close to their chests. However, it is significant that the Lighting Research Center in Troy, New York is holding a two-day workshop on September 20 and 21, the first of its kind in North America, on the design of architectural luminaires incorporating LEDs and on how to design a lighting installation using LEDs.
Skylights improve sales
A recent study involving over 100 outlets of a California retail chain (Skylighting and Retail Sales, by Heschong Mahone Group for Pacific Gas and Electric Company, San Franciso, August 20, 1999) concluded that skylights have a significant and positive correlation with improved sales. It was found that the skylights had the greatest effect on sales of any of the variables considered. There may have been other factors behind the dramatically higher sales, but there was no obvious candidate. According to the study, all other things considered the addition of skylighting to big, single store retail centres will result, on average, in a 40% increase in sales.
The study does not explore why skylighting resulted in increased sales. One of the reasons could have been an illumination level that was two to three times that provided by artificial lighting. Another could have been the positive responses of customers who were interviewed in stores with skylights. These were along the lines of “The store feels cleaner” and “It feels more spacious, more open.”
Quality lighting is clearly considered part of the merchandising policy of the chain in question. Most of the artificial lighting is fluorescent, coupled with display lighting, and carefully thought out in relation to the skylights. Photosensors control the electric lights under the skylights, and the retailer claims that the company has realized significant savings in the use and associated cost of electricity.
The problem of how to prevent a skylight appearing black at night remains. One approach to the solution has been to apply a glass frit of translucent white dots that appear opaque at night. By day, some light is transmitted through the dots in addition to that which enters between them. At Herzog and de Meuron’s Tate Modern, the bottom of each skylight is glazed with a translucent material while a battery of fluorescent lamps of different white hues is mounted on the sides of the skylights. The mix of colours is automatically adjusted to match that of the fading daylight.
New fluorescent lamps will include a range of coloured lamps, lamps with an integral acrylic safety sheath intended for use over food counters, and improved T5 (5/8″ diameter) lamps. From my own observations, it seems that this last lamp is not yet as widely used for store lighting in Canada as it is in Europe.
The fluorescent lamps most likely to be of general interest to store operators are the T8 (one-inch diameter) lamps that incorporate very significant advances in lamp technology made over the last quarter century aimed at improving lamp efficiency. These T8 lamps, which have good qualitie
s in terms of colour and light maintenance, can be used as a direct replacement for existing 32-watt lamps with a consequent savings of 6% in energy consumption with no reduction in light. Alternatively, they can be used in combination with a dedicated two-lamp or four-lamp ballast and the above energy savings will be almost doubled.
The lamp manufacturers, with an eye to the high cost of labour just to replace a lamp in a store, note that the above lamps have a rated life of 36,000 hours at 12 hours per start.
Metal halide lamps
Metal halide (MH) lamps rated at 250 and 400 watts have long been used to provide ambient light in large stores. Unfortunately, the lamps’ colour rendering properties were not the best and, over time, the colour of the lamps themselves changed so that adjacent lamps looked to be of different colours. These difficulties have been overcome in new 250- and 400-watt MH lamps. Improved lamp technology–particularly the use of ceramic arc tubes–has resulted in long life lamps with a CRI of over 90 and which do not change colour as their predecessors did. Similar MH technology is used in lower wattage lamps and reflector lamps.
Freedom of choice
Stores are always looking for ways to get their customers to come back. The innovative use of light is fundamental to this effort. It helps to define the style of a shop, from the convenience store with its ceiling lined with fluorescent tubes creating a “nightless” space that discourages lingering, to a store with an atmosphere aimed at persuading customers to browse. And malls–no longer just neutral corridors between shops–feature a wide variety of lighting effects.While keeping up to date with an ever-expanding range of lighting equipment requires considerable effort, the enormous variety of lighting currently available gives designers immense creative freedom.
Ernest Wotton, P. Eng., is a Toronto-based lighting consultant and designer.