The organic light-emitting diode (OLED) is an area light source, and its primary competing technology is the edge-lit light-emitting diode (LED) panel. Both technologies are similar in shape and appearance, but there is little understanding of how people perceive discomfort glare (DG) from area sources. The objective of this study was to evaluate the DG of these two technologies under similar operating conditions. Additionally, two existing DG models were compared to evaluate the correlation between predicted values and observed values. In an earlier study, we found no statistically significant difference in human response in terms of DG between OLED and edge-lit LED panels when the two sources produced the same luminous stimulus. The range of testing stimulus was expanded to test different panel luminances at three background illuminations. The results showed no difference in perceived glare between the panels, and, as the background illumination increased, the perceived glare decreased. In other words, both appeared equally glary beyond a certain luminance and background illumination. We then compared two existing glare models with the observed values and found that one model showed a good estimation of how humans perceive DG. That model was further modified to increase its power.
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.
Light-emitting diode (LED) technology is presently targeted to displace traditional light sources in backlighted signage.
The literature shows that brightness and contrast are perhaps the two most important elements of a sign that determine its
attention-getting capabilities and its legibility. Presently, there are no luminance standards for signage, and the practice
of developing brighter signs to compete with signs in adjacent businesses is becoming more commonplace. Sign
luminances in such cases may far exceed what people usually need for identifying and reading a sign. Furthermore, the
practice of higher sign luminance than needed has many negative consequences, including higher energy use and light
To move toward development of a recommendation for lighted signage, several laboratory human factors evaluations
were conducted. A scale model of a storefront was used to present human subjects with a typical red channel-letter sign
at luminances ranging from 8 cd/m2 to 1512 cd/m2 under four background luminances typical of nighttime outdoor and
daytime inside-mall conditions (1, 100, 300, 1000 cd/m2), from three scaled viewing distances (30, 60, 340 ft), and either
in isolation or adjacent to two similar signs. Subjects rated the brightness, acceptability, and ease of reading of the test
sign for each combination of sign and background luminances and scaled viewing distances.
This paper outlines two parts of a study designed to evaluate the use of light-emitting diodes (LEDs) in channel-letter signs. The first part of the study evaluated the system performance of red LED signs and white LED signs against reference neon and cold-cathode signs. The results show a large difference between the actual performance and potential savings from red and white LEDs. Depending on the configuration, a red LED sign could use 20% to 60% less power than a neon sign at the same light output. The light output of the brightest white LED sign tested was 15% lower than the cold-cathode reference, but its power was 53% higher. It appears from this study that the most efficient white LED system is still 40% less efficient than the cold-cathode system tested. One area that offers a great potential for further energy savings is the acrylic diffuser of the signs. The acrylic diffusers measured absorb between 60% and 66% of the light output produced by the sign. Qualitative factors are also known to play an important role in signage systems. One of the largest issues with any new lighting technology is its acceptance by the end user. Consistency of light output and color among LEDs, even from the same manufacturing batch, and over time, are two of the major issues that also could affect the advantages of LEDs for signage applications. To evaluate different signage products and to identify the suitability of LEDs for this application, it is important to establish a criterion for brightness uniformity. Building upon this information, the second part of the study used human factors evaluations to determine a brightness-uniformity criterion for channel-letter signs. The results show that the contrast modulation between bright and dark areas within a sign seems to elicit the strongest effect on how people perceive uniformity. A strong monotonic relationship between modulation and acceptability was found in this evaluation. The effect of contrast seems to be stronger than that of spatial frequency or background luminance, particularly for contrast modulation values of less than 0.20 or greater than 0.60. A sign with luminance variations of less than 20% would be accepted by at least 80% of the population in any given context.
Light exposure regulates several circadian functions in normal humans including the sleep-wake cycle. Individuals with Alzheimer’s Disease (AD) often do not have regular patterns of activity and rest, but, rather, experience random periods of sleep and agitation during both day and night. Bright light during the day and darkness at night has been shown to consolidate activity periods during the day and rest periods at night in AD patients. The important characteristics of bright light exposure (quantity, spectrum, distribution, timing and duration) for achieving these results in AD patients is not yet understood. Recent research has shown that moderate (~18 lx at the cornea) blue (~470 nm) light is effective at suppressing melatonin in normal humans. It was hypothesized that blue light applied just before AD patients retire to their beds for the night would have a measurable impact on their behavior. A pilot study was conducted for 30 days in a senior health care facility using four individuals diagnosed with mild to moderate levels of dementia. Four AD patients were exposed to arrays of blue light from light emitting diodes (max wavelength = 470 nm) in two-hour sessions (18:00 to 20:00 hours) for 10 days. As a control, they were exposed to red light (max wavelength = 640 nm) in two-hour sessions for 10 days prior to the blue light exposure. Despite the modest sample size, exposure to blue LEDs has shown to affect sleep quality and median body temperature peak of these AD patients. Median body temperature peak was delayed by approximately 2 hours after exposure to blue LEDs compared to exposure to red LEDs and sleep quality was improved. This pilot study demonstrated that light, especially LEDs, can be an important contribution to helping AD patients regulate their circadian functions.