Lighting Research Center Lighting Research Center
    Volume 7 Issue 5
September 2003 (revised March 2005)    
Full-Spectrum Light Sources
color rendering index (CRI) - A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural. correlated color temperature (CCT) - A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT. efficacy - The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt. minimal erythema dose (MED) - The quantity of ultraviolet radiation (expressed in Joules per square meter) required to produce the first perceptible, redness reaction on human skin with clearly defined borders. MED can vary significantly depending on factors such as skin pigmentation. x-bar - Color matching function x-bar, y-bar, z-bar are used to define the color-matching properties of the CIE 1931 standard observer. In 1931, CIE defined the color-matching functions x-bar, y-bar, z-bar in the wavelength range from 380nm to 780 nm at wavelength intervals of 5nm. spectral power distribution (SPD) - A representation of the radiant power emitted by a light source as a function of wavelength. positive affect - Relatively mild shifts in current mood in a positive direction.
What are the disadvantages of full-spectrum light sources?

Other than potential damaging effects on architectural materials from full-spectrum light sources that produce ultraviolet (UV) radiation, the primary disadvantages of full-spectrum lamps are economic. Full-spectrum lamps are often priced several times higher than conventional lamps. For example, in Troy, New York, a four-foot T12 lamp costs between $1.25 and $3.60, while a full-spectrum four-foot T12 lamp costs $14.90.

In comparing spectral power distributions (SPDs) for this report, NLPIP found that one of the major lamp manufacturers offers a $5.86 four-foot T12 fluorescent lamp with a spectrum nearly identical to that of the $14.90 full-spectrum lamp, but the manufacturer of the less expensive lamp does not market it as a full-spectrum lamp. Figure 3 compares the spectra of the full-spectrum lamp costing $14.90 and the $5.86 lamp.

Figure 3. Spectral comparison of a claimed full-spectrum lamp and a fluorescent lamp not marketed as full-spectrum.

Most claimed full-spectrum lamps are also relatively less energy-efficient. Full-spectrum T12 fluorescent lamps have an efficacy about 30% to 40% lower than conventional triphosphor fluorescent lamps, and thus must consume more energy to provide comparable light levels. Table 1 summarizes lamp performance data for several commercial lamp types, and includes lamp efficacy ratings.

Table 1: Performance characteristics of several popular light sources.
Light Source CCT CRI FSI Efficacy (lm/W)
Equal Energy Spectrum 5457 95 0 N/A
5500K 5500 100 0.35 N/A
11000K 11000 100 2.0 N/A
1000W 5900 96 1.2 22
60-100W A-lamp 2800 100 5.3 17
60W GE Reveal A-lamp 2789 78 5.6 11
Light-Emitting Diode (LED)
White LED 5000 78 5.2 13
RGB (615nm/525nm/470nm) LED mix* 4400 65 9.8 22
RGB (640nm/525nm/470nm) LED mix* 4200 26 8.2 22
Compact Fluorescent
15-20W 2700-3000K 2800 82 11 61**
15-20W 5000K 5000 85 5.9 47**
15W Verilux CFS15VLX 5777 78 5.6 60**
T8 Fluorescent
32W 3500K 3300 84 8.3 92
32W 5000K 4800 87 6.4 88
32W Lumiram Lumichrome 1XX 5960 93 4.7 73
32W Verilux F32T8VLX 6369 85 6.2 88
T12 Fluorescent
40W 5000K 4900 91 1.8 56
40W Duro-Test Daylight 65 6588 93 1.8 53
40W Duro-Test Vita-Lite 5500 5159 88 1.4 55
40W Lumiram Lumichrome 1XC 5207 92 1.6 59
40W Verilux F40T12VLX 5833 94 1.4 53
Metal Halide
320-400W / Warm color 3600 68 5.0 92
175-400W / Cool color 4300 61 4.3 90
Ceramic Metal Halide
35-70W / Warm color 2900 84 6.5 79
100W / Warm color 3100 81 5.1 93
100-150W / Cool color 4100 93 1.5 90
Mercury Vapor
175-400W / Coated lamp 3900 43 5.5 54
400W / Clear lamp 5900 15 9.6 53
High Pressure Sodium
200-400W 2000 12 22 120
Low Pressure Sodium
180W 1800 0 52 180
Light sources displayed in red are claimed as full-spectrum by their manufacturers. CCT, CRI, and FSI values for these light sources were calculated from SPD measurements performed at the Lighting Research Center; efficacy values were calculated from manufacturers' data. Entries for other sources are representative values.

* The values in parentheses represent the peak outputs of the respective red, green and blue LEDs mixed to create this light source.

** Efficacy values for CFLs include losses from integral ballasts.


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