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 benefits are claimed for full-spectrum light sources?

A fluorescent or incandescent lamp claimed to be full-spectrum can cost several times as much as one with a nearly identical spectral power distribution (SPD) that is not identified as full-spectrum. What benefits does a consumer get for that extra money? NLPIP reviewed the promotional claims for full-spectrum light sources from manufacturer and retailer web sites, and found a diversity of claimed benefits, including:

  • Improves color perception
  • Improves visual clarity
  • Improves mood
  • Improves productivity
  • Improves mental awareness
  • Improves retail sales
  • Improves plant growth
  • Improves results of light therapy in treating seasonal affective disorder (SAD)
  • Improves results of light therapy for sleep disorders
  • Improves scholastic performance of students
  • Improves vitamin D synthesis in the body
  • Reduces incidence of dental decay

In order to assess the impact of these manufacturer claims on the perceptions of lighting specifiers, NLPIP conducted an online survey in April 2003. A total of 252 lighting specifiers, including electrical contractors and facility managers were asked, "Compared to other types of lighting, please indicate how you think full-spectrum light sources impact the following…" Figure 2 shows the results of the online survey.

Figure 2. Perceived benefits of full-spectrum light sources among lighting specifiers
Because some participants did not respond to all survey questions, the responses for each perceived benefit may not add up to 100%.

Overall, the survey respondents believed in most of the claimed benefits of full-spectrum light sources. For nine of the twelve potential benefits, more than 50 percent of the respondents believed that full-spectrum light sources have a positive effect. More people believed in a positive effect on color perception than any of the other potential benefits, with 86 percent responding positively. The least believed claim was improved dental health, with only 15 percent responding that full-spectrum light sources affected it positively. For all claimed benefits, less than 4 percent of the respondents believed that full-spectrum light sources actually had a negative impact.

As registrants of NLPIP's web site, the audience that participated in this survey probably has lighting technical knowledge greater than that of the average person, but similar to that of the typical lighting specifier. The results of this survey indicate that the marketing message from manufacturers of full-spectrum light sources appears to be getting through to its intended audience of lighting specifiers.


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