The Advantages of Full Spectrum Lighting

This article appeared in the January, 1990 issue of CEE NEWS. The Premier Magazine Covering Electrical Construction Industry Products & News. The unique characteristics of this lighting technology are explained...
By Ambrose Paul Wasdyke, Jr.

INSIGHT into new lighting technology, such as full spectrum light, is important for electrical contractors concerned with gaining a competitive edge, as well as increasing the value of services provided to customers. Today, electrical contractors must familiarize themselves with many aspects of lighting technology. This includes understanding the characteristics of the type of lighting being installed---traditionally, the responsibility of interior designers, architects, and space planners. While it may not be necessary to gain as high a level of expertise in these areas, additional lighting knowledge can make the electrical contractor an important information resource to the customer and other members of the design team. This type of additional input will contribute to the success of the overall lighting system. A successful lighting system not only depends on how well the system is wired, but the level of customer satisfaction regarding the quality of the light. The ability to improve the final result reflects well on the electrical contractor's customer relations as well as his professional relations. Full spectrum light is an excellent example of how unique characteristics of lighting can affect the installation of a lighting system. Because of its far greater spectral power distribution as compared to standard cool white fluorescent light (sometimes called distorted spectrum light), full spectrum light required a different approach to measurement and fixture placement.

While full spectrum light may be new to many people, it is not a new concept. Full spectrum light simulates the full spectral power distribution range (both visible and ultraviolet) of natural outdoor light. Our eyes evolved in full spectrum light. It is the light in which we see best. Standard cool white fluorescent light does not provide the type of light conducive for high color rendering. Lack of good color rendering is one reason people view objects next to windows to see colors and textures more clearly, although the light level in the room may seem adequate. The advantages of full spectrum light in the indoor environment include perceiving fine details clearer; performing visually demanding tasks (such as color matching) more effectively; reducing glare, thereby lessening eye fatigue and strain; and reducing maintenance and replacement cost due to its long life features. Because of the different qualities of light, it is not surprising that devices, such as illuminance meters (footcandles) designed to measure incandescent light, are inaccurate when measuring full spectrum light. Illuminance meters are still relied upon today because not long after electric light sources were invented, a set of lighting standards was established to determine the adequacy of our indoor environments. In 1924, the International Commission on Illuminance established the footcandle as a measurement of illuminance or light quality. Since then, illuminance meters or light meters have been used to measure illuminance in footcandles only and are not completely accurate for measuring light across all spectra.

A footcandle reading is a measurement of illumination equal to one lumen per square foot or the amount of light that is spread over a square foot surface by one candle when all parts of the surface are exactly one foot from the candle light source. Footcandle levels only indicate the amount of illumination or light intensity): which is not necessarily an indication of visual performance, as is the case with full spectrum light. Tests by the author's company show that light from a high color rendering lamp, such as full spectrum light, provides equal visual acuity at 75% to 80% of the footcandle level of a standard high lumen-output lamp such as cool white fluorescent light. In fact, lower wattage full spectrum light can be substituted for cool white lamps of higher footcandles and actually improve visual acuity. Despite its limited utility, the footcandle has persisted in the electrical contracting industry as a dominant factor in the measurement of illumination. As seen with full spectrum light, other aspects of light must be considered. With Color temperature, spectra of a lamp, the first step is to measure the spectral power distribution. Once this has been accomplished, the color temperature and color rendering can be determined.

Spectral power distribution (quantity of light or power emitted at each wavelength) is used to determine color temperature, color rendering index and lumen output of a particular lamp. The SPD of each major lamp type must be measured by an optical instrument called a spectroradiometer to determine the quality and application purposes of lighting systems. The spectroradiometer is a photometric laboratory device that breaks up the light into its individual wavelengths and measures the energies of the light spectrum. Because of the size and high cost of this piece of equipment, the spectroradiometer is not a practical field tool for electrical contractors. A better way to determine technical specifications for the proposed lighting is to contact the regional sales office or the sales engineering department of the manufacturer. The color temperature of a light source is measured to determine light quality. Color temperature has no relationship to room temperature and pertains only to the appearance of the light source. Color temperature refers to the temperature in degrees Kelvin at which a black body, a theoretical perfect radiator, would have to be heated to match most nearly the perceived color of the light source. For example, most cool white fluorescent lights cast a yellowish or green tint and measure between 4200K and 4500K.