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.