In the past decade, there has been increased interest in energy-efficient lighting as energy resources become higher in
demand. Street lighting and outdoor lighting are applications that are rapidly changing from the incumbent high-pressure
sodium (HPS) to newer technologies such as light-emitting diode (LED) or induction-type lamps. There is evidence that
certain populations believe LED streetlights and area lights to produce more glare than HPS luminaires. A number of
differences exist between new and traditional light sources besides efficiency. These include spectral power distribution
(SPD), source luminance, beam intensity distribution, and the number of sources needed to achieve intended light levels.
Many field studies and laboratory studies have shown a relationship between glare and SPD, with most studies
suggesting that sources more weighted in short wavelengths have an increased likelihood of discomfort glare. A study to
assess the effect of different SPDs on perception of discomfort glare was conducted. Subjects were shown a white-light
LED array against a luminous background with one of three different SPDs (blue, white, or yellow). As well, different
intensities of light from the array and from the background were used. For the range of conditions evaluated, the
presence of any luminous background significantly reduced the perception of discomfort glare from the LED array. The
blue background reduced perception significantly less than the white or the yellow backgrounds. The implications for
solid-state lighting systems such as outdoor array lighting are discussed.