Enlightened Illumination

Rumor has it that butchers put beef under red lights to make it look better. That makes sense: Lights that generate more nonabsorbing wavelengths do enhance the color of the object being lit. Beef doesn’t absorb red, so putting a filet mignon under lights that generate a higher-than-natural daylight red content—for example, incandescent lights—gives it an even more appealing red color.

Rubies and red “flame” spinels ignite the same way under incandescent lights. The tungsten MR16 mini spotlights highlighting many jewelry showcases are red-producing lights. They typically distribute a lot of red and yellow wavelengths, but not much blue or green. Unless other lights balance the overabundance of red, the gem’s fire will be extinguished when a customer takes it outside. The difference becomes even more dramatic when the customer shows it to friends back at the office, an area commonly lit with diffused “cool white” fluorescent lights. These have an overabundance of blue and green and very little red, which can make a red gem look dreadful.

“A lady shouldn’t be shocked when she wears her ruby outside the store,” says Jan Goodman, a gem dealer and lighting advocate in Los Angeles. Goodman, who has been selling gems and lights for approximately 20 years, says he got into the lighting business because jewelers were returning goods, saying the color wasn’t what they wanted. Goodman knew store lighting was the culprit.

A light for all seasons. What Goodman and others in the gem business have been searching for is a single light that makes all gems look the way they do in daylight. That’s a tall order. Average natural daylight—composed of light coming directly from the sun and indirectly from the sky—has a balanced spectrum throughout most of the visible light wavelengths. This balanced (or “flat”) spectrum renders colors perfectly. Artificial lights try to emulate natural light to give clothes, skin, cars, jewelry, and other products the same look they would have under the sun.

Duplicating the flat spectrum of natural light won’t, by itself, duplicate natural daylight. That’s because natural light is always changing: the sun rises and sets, weather conditions and pollution cause interference, and direct sunlight differs dramatically from indirect sunlight seen through skylights or windows.

For example, direct morning sunlight is packed with yellow and red wavelengths, but indirect morning light seen indoors at a north-facing window is saturated in blue. And these kinds of differences continue throughout the day.

Color by Kelvin. Most jewelers will tell you the proper daylight equivalent is “north daylight,” which in the northern hemisphere is considered the most consistent of all light. Thus, most gems are color-graded at north-facing windows or under lamps thought to be equivalent to north daylight. But complications arise: Both morning and late afternoon north daylight are much more blue than noontime north daylight.

To define different daylights, experts measure the color temperature of the light in degrees Kelvin—actually a visual measurement of an iron bar’s changing appearance as it’s heated. Low Kelvin temperature-rated bulbs—3,000°K to 4,000°K—appear reddish. High Kelvin temperature bulbs (6,500°K to 7,500°K) look bluish. (The hotter the iron bar gets, the bluer it appears; it eventually turns blue-white.) Daylight lamps are Kelvin-rated between 5,000° and 7,500°.

For example, “7,500°K north daylight” is equivalent to the light produced by a moderately overcast sky—a reflected blue sky. The best average daylight is considered 6,500°K north daylight. It’s the worldwide standard for the automotive industry and the international standard in Europe, the Far East, and South America (although 7,500°K probably comes closer to average North American daylight). However, noon north sky daylight is measured at 5,000°K and is the standard for the graphics art industry. It could be argued that the noon 5,000°K indirect sky daylight is the best daylight time and temperature, since the light’s spectral output is more even across the board compared with that of the more bluish 6,500°K or 7,500°K daylight.

Rendering color. Kelvin temperature doesn’t indicate how well a light renders an object’s color. The lighting industry uses the Color Rendering Index (CRI) to describe the extent to which an artificial light source is able to render the “true” color of objects as seen by natural outdoor sunlight, which has a CRI of 100. The closer the CRI of a light bulb is to 100, the more accurately it’s supposed to render colors. Thus, a bulb with a high CRI appears to be a good choice for standard store lighting. But the CRI, like Kelvin temperatures, can be misleading.

The popular tungsten/halogen MR16 display lamp, for example, can have a CRI as high as 99.3. But even bulbs with high CRI ratings display color best only at a given color temperature.

Color-corrected MR16s are typically sold in 3,500°K, 4,100°K, and 4,700°K—not the equivalent of the standard north daylights mentioned above but more like direct early morning/late afternoon daylight lighting, high in red content, with very little blue. And CRI ratings for lights below

5,000°K are compared with tungsten light, not natural daylight. Lights above 5,000°K (measured against natural daylight) can have a lower CRI than most MR16s but have better color rendering capability. But don’t pull down your MR16 lights just yet.

Ingredients not on the box. The key to understanding how a light will make your gemstones look may be spectral output curves, or “spectral power distribution” (SPD). SPDs show visible light output in wavelengths through the visible light spectrum, from 400 nm to 700 nm. Natural light has specific SPDs, depending upon Kelvin temperature (including time of day and whether the light is direct or indirect). Experts compare the SPDs of natural daylight and light bulbs of the same Kelvin temperature. Daylight at 5,000°K, 6,500°K, and 7,500°K has a relatively flat, broad, full-spectrum output. Typical cool white “daylight” fluorescent tubes are far from equivalent to actual daylight: They have a Kelvin temperature of 4,250°K, a CRI of only 62, and they show significant spikes in the blue, green, and yellow regions of the SPD. These spikes cause the light to unnaturally enhance blue, green, and/or yellow gems, and wreak havoc on red gems.

Arguably the closest match to natural daylight is GretagMacbeth’s filtered tungsten/halogen SpectraLight. The curve of the D65 (6,500°K) is similar to that of natural daylight at 6,500°K, showing no significant spikes. It has a CRI rating of 94. The SpectraLight D50, a 5,000°K lamp, is comparable to daylight at 5,000°K, and both have a more even, flat spectral output than the other two daylight temperatures. Unlike any other lamp, the D50 doesn’t offer an advantage or disadvantage to any color under its light. But lighting a store with D50s is expensive, both in the cost of the bulbs and the air conditioning needed to cool the hot lights.

Knowing Kelvin temperature and SPD can help you make an informed decision, but SPD information isn’t easy to come by. You probably won’t find it on the box of lights at Ace Hardware. Bulb manufacturers usually provide spectral analysis of light bulbs in SPDs only upon request.

Cheap tubes, ugly rubies. The more common incandescent spotlights, like the MR16 tungsten/halogens at your local hardware store, will enhance a ruby—or as Goodman says, “make it dance.” But he says they’re too yellow to be used alone to buy or sell gems. He points out that while rubies may look better, emeralds and sapphires lose their color under these spotlights. On the other hand, most cool white fluorescent lights contain an abundance of blue and green, making sapphires, emeralds, and most other blue or green stones look pretty good, but rubies, rubellites, and other red stones will look awful.

Goodman uses Excella fluorescent lamps, which he says provide the look of Bangkok daylight. He says the rubies he buys in Bangkok look as good in his office as when he bought them. “Sotheby’s and Christie’s auction houses both use the Excella in their preview rooms,” he points out. “It’s a very pleasant light.”

Both the Excella fluorescent lamp and the GretagMacbeth filtered tungsten/halogen are categorized as “full-spectrum lamps,” but their SPDs are somewhat different. The Excella has a touch more red, which correlates with Goodman’s description of daylight in Bangkok.

But getting good lighting into gem dealers’ offices isn’t easy. “I see these cheap fluorescent lights in some dealers’ offices, and when I ask them about getting better lights, they say, ‘No thanks, I’m used to it.’ But have you been in some of those offices?” Goodman asks. “Your hand is that yellowish-green color. It’s not natural. I ask them if they buy much ruby and they say, ‘Rubies don’t sell well.’ Of course not. Rubies look purple—not red—under these lights.”

Technically speaking, under cool white fluorescent lights, rubies appear grayish and desaturated, which makes them dull and unappealing. So what’s the answer? “You need a light that’s good for everything,” says Goodman.

“People spend good money on ads, displays, a lighting designer, and even buy high-tech halogens, but they’re so cheap about putting in good fluorescent lighting. It really makes a difference when you have good lights,” says Goodman. “But for many dealers, their office lights are those ‘cool whites’ that cost $3 or $4 apiece and are used for parking garages and men’s rooms. A good lamp will give you 20 times the light for [just] three times the cost.”

Sometimes, store design doesn’t allow for fluorescent lighting. But these lights are important and jewelers should try to find a way to incorporate them over their showcases.

The morning blues. Why is it good to have a little more red in your lights? If you examine daylight carefully, direct daylight in the morning looks yellow, but by noon, the light becomes bright white. As the sun begins to set, the color of daylight shifts back into the yellow, and just before sunset, the light becomes more reddish. Rubies, of course, look better in a more reddish light, and jewelers who buy and sell rubies know what time of day the rubies will look best and when they look their worst.

Medium blue is dark in Alaska. Daylight in different regions of the United States can show gem colors differently. For instance, dealers in Seattle will be looking for lighter colored gems than those in Southern California, because daylight is brighter in the south. Bright sunlight makes darker colors brighter, while the same dark stones remain dark under the moderate sunlight of the north.

Medium dark-blue sapphires look best in clear weather, reflecting blue sky. Light-blue sapphires look best outside in cloudy weather or indirect evening sky in the south, which gives them a more saturated appearance, but noontime clear skies in the north will do the same thing. Dark-blue sapphires look better under the Los Angeles haze and look even darker under the clear and darker-blue big skies of Montana.

In the land of the midnight sun, average daylight varies tremendously compared with that of daylight in Tucson, for example. But Rex Thompson of Alaskan Gold & Platinum Design in Juneau doesn’t see much difference. “We’re only about 700 miles north of Seattle. We’re also about 30% more overcast than Seattle,” says Thompson, who is trying to find good lighting for his store. “We’re looking at the Solux 4,100K. It’s such a cold light that it makes diamonds look wonderful, but platinum looks too cold. And everything else looks surreal. Yellow gold actually looks bad.”

The color output of store lighting really can influence sales. “I just recently did some work for [apparel retailer] Ann Taylor,” says Nick Lena, illumination engineer and lighting product manager for GretagMacbeth. “In certain stores, certain colors are popular. [For] those that used track lighting, MR16s, red colors were the most popular. But in the stores that had fluorescent or metal halide fixtures, blues were very popular.” And the tungsten halogen MR16 eliminates UV, notes Lena. If you have Burmese rubies, which get some of their vibrant rich color from UV fluorescence, MR16s won’t give them their “look.”

“I’ve returned some gems I bought in Tucson because they just didn’t look the same,” says Lena. “The sun is different. I had a padparadscha—the most delicate pinky-orange. But up here, it was mostly just a washed-out pink.”

“We do a lot with all colors of sapphire,” says Thompson. “We carry imperial topaz and a variety of tourmalines, and garnets.” In fact, Thompson notes that they sell more grape garnet than anything. “That’s because there’s more red content in their daylight,” says Lena. “The reds pop.” But Thompson says that on his recent trip to Tucson, he unconsciously purchased a lot more lighter-toned gems than in the past.

“Because daylight changes—during the day, the seasons, the latitude—this is all justification for having a standardized light source,” says Lena. “Then everything would really look the same when you’re in other places, like Alaska, or Tucson, or Bangkok. You just can’t depend on real daylight.”

Some ruby dealers know that weather as well as time of day will affect a gem’s look. Cloud cover will enhance a ruby’s color (less sky blue), whereas clear blue skies will give the stone a purplish color. Light-colored ruby looks best under dim lighting (candlelight, low wattage incandescent lights, sunrise or sunset—roughly equal to 1,800°K), and dark ruby looks best when the light is brightest—i.e., direct noonday sun. In fact, because of the smog and latitude of Bangkok, it is said that ruby that looks dark in Thailand will look even darker in the United States. Smog will actually lighten a blue sky. In cities with less smog, the darker-blue sky will dull and darken a red gem.

To make matters even more complicated, light takes on a totally different color when seen indirectly—for example, inside at a north-facing window. In the morning, the light is bluish; from 11 a.m. to 1 p.m. it’s a lighter, whiter blue. It shifts back to a more bluish color late in the afternoon.

No single perfect light. Dick Hughes is the ruby and sapphire expert at Pala International, a colored gem wholesaler in Fallbrook, Calif. “We use a variety of light sources for buying,” Hughes explains, “including daylight (through skylights in our building), fluorescent tubes, and halogen bulbs. Obviously, the idea is to examine a stone under a variety of conditions to see how it will look. With experience—of which we have a lot—one can generally predict how a stone will look. The type of stone (ruby vs. spinel vs. garnet; sapphire vs. tanzanite) plays a big part, as does the origin—say, Kashmir vs. Burma in sapphire.”

But Hughes finds himself in the same predicament as Goodman when sending goods out. “Since we send stones to our clients, we cannot control their lighting but will often counsel them on what type of light to use or avoid when showing their clients the stones,” he says. “Obviously, we want our stones to look good when they are shown, in the same way a car dealer will wash and clean his product before putting it out on the lot.”

Lena admits that “there is no perfect light source. Jewelers need the efficiencies of well-balanced florescence, with the sparkle of filtered tungsten halogen. Directionality of the light is critical.” Lena says that even fluorescent daylight lamps (5,000-6,500°K) with high CRI and few spectral peaks won’t make gems sparkle. You need the direct spotlight that filtered tungsten halogens can provide.

Lena, who has given presentations to General Motors, Chrysler, and Volkswagen, compares the sparkle of a gem to metal-flake paint in cars: “You don’t see the glitter of the paint if you don’t have direct light on the car.”

GretagMacbeth has developed a light box that contains all the lights needed to simulate different times and temperatures of daylight as well as indoor office lighting and home incandescent lighting. The $4,400 SpectraLight viewing booth lights can be programmed to shift through a sequence of lighting conditions a gem might encounter during a normal 24 hours, including sunrise and sunset, morning and afternoon, the cool white fluorescent lighting of an office building, and the incandescent lighting of home. For jewelers matching rubies, emeralds, sapphires, and tanzanites, it makes sense to check the color of a gem at all times of day.

While Lena knows that many storeowners will not replace entire ceilings with corrected-light sources, he does suggest that they provide an area for critical evaluation. “Color is perceived as quality,” says Lena. And good-quality lighting that renders the true color of your gems will show your customer the real quality of your merchandise.

Thanks to Jan Goodman, Los Angeles, (310) 888-8873, and Nick Lena, GretagMacbeth, www.gretagmacbeth.com.