Ms. Vasudha Ramamurthy Profile

Vasudha Ramamurthy

at Rensselaer Polytechnic Institute

SPIE Involvement:

Author

Publications (2)

Proceedings Article | 26 January 2004 Paper

Evaluation of light-emitting diodes for signage applications

Jean Paul Freyssinier, Yutao Zhou, Vasudha Ramamurthy, Andrew Bierman, John Bullough, Nadarajah Narendran

Proceedings Volume 5187, (2004) https://doi.org/10.1117/12.507875

KEYWORDS: Light emitting diodes, Neon, Modulation, Manufacturing, Diffusers, Light sources and illumination, Spatial frequencies, Temperature metrology, Lamps, Transmittance

Read Abstract +

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.

Proceedings Article | 26 January 2004 Paper

Determining contrast sensitivity functions for monochromatic light emitted by high-brightness LEDs

Vasudha Ramamurthy, Nadarajah Narendran, Jean Paul Freyssinier, Ramesh Raghavan, Peter Boyce

Proceedings Volume 5187, (2004) https://doi.org/10.1117/12.509195

KEYWORDS: Light emitting diodes, Visualization, Spatial frequencies, Light sources, Contrast sensitivity, Light sources and illumination, Image quality, Light, Image analysis, Blue light emitting diodes

Read Abstract +

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years