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.
Solid-state lighting (SSL) offers a new technology platform for lighting designers and end-users to illuminate spaces
with low energy demand. Two types of SSL sources include organic light-emitting diodes (OLEDs) and light-emitting
diodes (LEDs). OLED is an area light source, and its primary competing technology is the edge-lit LED panel. Generally,
both of these technologies are considered similar in shape and appearance, but there is little understanding of how people
perceive discomfort glare from large area light sources. The objective of this study was to evaluate discomfort glare for
the two lighting technologies under similar operating conditions by gathering observers’ reactions. The human factors
study results showed no statistically significant difference in human response to discomfort glare between OLED and
edge-lit LED panels when the two light sources produced the same lighting stimulus. This means both technologies
appeared equally glary beyond a certain luminance.
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.
Lighting plays an important role in supporting retail operations, from attracting customers, to enabling the evaluation of
merchandise, to facilitating the completion of the sale. Lighting also contributes to the identity, comfort, and visual
quality of a retail store. With the increasing availability and quality of white LEDs, retail lighting specifiers are now
considering LED lighting in stores. The color rendering of light sources is a key factor in supporting retail lighting goals
and thus influences a light source's acceptance by users and specifiers. However, there is limited information on what
consumers' color preferences are, and metrics used to describe the color properties of light sources often are equivocal
and fail to predict preference. The color rendering of light sources is described in the industry solely by the color
rendering index (CRI), which is only indirectly related to human perception. CRI is intended to characterize the
appearance of objects illuminated by the source and is increasingly being challenged because new sources are being
developed with increasingly exotic spectral power distributions. This paper discusses how CRI might be augmented to
better use it in support of the design objectives for retail merchandising. The proposed guidelines include the use of
gamut area index as a complementary metric to CRI for assuring good color rendering.
The light-emitting diode (LED) is a rapidly evolving, energy-efficient light source technology that holds promise to
address the increasing need for energy conservation. However, the common belief that a high-efficacy light source
equates to lower energy demand in application is incorrect. Generally, when a new light source technology replaces an
existing light source in an application and claims energy savings, the inherent assumption is that all of the requirements
of the application are met. In the case of directional lighting applications, what matters ultimately is the amount of
luminous flux illuminating the task area. Therefore, when quantifying the performance of a luminaire, ideally one must
consider only the amount of flux reaching the task area and the total power demanded.
The objective of this paper is to introduce an alternative concept, application efficacy. This paper will demonstrate the
concept's usefulness and proposed metrics for three different lighting applications-under-cabinet task lighting,
refrigerated display case lighting, and outdoor parking lot lighting-and show how it better relates to energy demand.
Details of laboratory experiments and software analysis along with data are presented for the three applications.
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.
A field study was conducted at three clothing stores to validate previous laboratory findings indicating that colored
LEDs used as background display lighting could: 1) lower the power demand of accent lighting by up to 50 percent; and
2) provide greater attention capture and visual appeal than current lighting practice.
Blue LEDs provided a colored background for window mannequins by illuminating white backdrops. Eliminating
fluorescent general lighting and reducing the number and wattage of halogen accent lamps in the display windows
reduced the lighting power demand by up to 50 percent. During an eight-week period, more than 700 shoppers rated the
attractiveness, eye-catching ability, comfort, and visibility of four different lighting conditions. The results of this field
study showed that by introducing color contrast between the displayed objects and the background, the power demand of
the accent lighting could be reduced by up to 50 percent without sacrificing visual appeal, visibility, ability to capture the
attention of shoppers, and the ability to see the colors of the objects on display. Furthermore, the sales of the products on
display were not affected by the 50 percent reduction in lighting.
Two life tests were conducted to compare the effects of drive current and ambient temperature on the degradation rate of 5 mm and high-flux white LEDs. Tests of 5 mm white LED arrays showed that junction temperature increases produced by drive current had a greater effect on the rate of light output degradation than junction temperature increases from ambient heat. A preliminary test of high-flux white LEDs showed the opposite effect, with junction temperature increases from ambient heat leading to a faster depreciation. However, a second life test is necessary to verify this finding. The dissimilarity in temperature effect among 5 mm and high-flux LEDs is likely caused by packaging differences between the two device types.
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-emitting diode (LED) technology is becoming the choice for many lighting applications that require monochromatic light. However, one potential problem with LED-based lighting systems is uneven luminance patterns. Having a uniform luminance distribution is more important in some applications. One example where LEDs are becoming a viable alternative and luminance uniformity is an important criterion is backlighted monochromatic signage. The question is how much uniformity is required for these applications. Presently, there is no accepted metric that quantifies luminance uniformity. A recent publication proposed a method based on digital image analysis to quantify beam quality of reflectorized halogen lamps. To be able to employ such a technique to analyze colored beams generated by LED systems, it is necessary to have contrast sensitivity functions (CSFs) for monochromatic light produced by LEDs. Several factors including the luminance, visual field size, and spectral power distribution of the light affect the CSFs. Although CSFs exist for a variety of light sources at visual fields ranging from 2 degrees to 20 degrees, CSFs do not exist for red, green, and blue light produced by high-brightness LEDs at 2-degree and 10-degree visual fields and at luminances typical for backlighted signage. Therefore, the goal of the study was to develop a family of CSFs for 2-degree and 10-degree visual fields illuminated by narrow-band LEDs at typical luminances seen in backlighted signs. The details of the experiment and the results are presented in this manuscript.