Although lighting systems powered by photovoltaic (PV) cells have existed for many years, they are not widely used, especially in lighting for buildings, due to their high initial cost and low conversion efficiency. One of the technical challenges facing PV-powered lighting systems has been how to use the dc power generated by the PV module to energize common light sources that are designed to operate efficiently under ac power. Usually, the efficacy of dc light sources is very poor compared to ac light sources. Rapid developments in LED lighting systems have made this technology a potential candidate for PV-powered lighting systems. This study analyzed the efficiency of each component of PV-powered lighting systems to identify optimum system configurations for different applications.
New concerns regarding the unwanted effects of lighting our nighttime environment (i.e., light pollution), and new efforts to design energy efficient roadway lighting installations, are changing the requirements of roadway lighting. These factors necessitate the need for different luminous intensity distributions with greater optical control than have traditionally been produced by roadway lighting fixtures. New requirements affecting the optical design of roadway lighting are presented. An example of a nonimaging optical design solution that addresses these requirements is given. Conclusions are then made about the challenges that lie ahead in the optical design of roadway lighting fixtures.
Although PV (photovoltaic)-powered lighting systems have existed for many years, they are not widely used, especially in lighting for buildings, due to their high initial cost and low conversion efficiency. One of the technical challenges facing PV-powered lighting systems has been how to use the DC power generated by the PV module to energize common light sources that are designed to operate efficiently under AC power. Usually, the efficacy of DC light sources is very poor compared to AC light sources. Rapid developments in LED (light-emitting diode) lighting systems have made this technology a potential candidate for PV-powered lighting systems. This study analyzed the efficiency of each component of PV-powered lighting systems to identify optimum system configurations for different applications.
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.