Technical Issues

Comparison between LED and incandescent signals

Survey participants were asked to describe any differences between LED and incandescent traffic signals of which they were aware. Predictably, 78% reported that LED signals used less energy than incandescent signals, and 52% stated that they also had longer life with resulting lower maintenance requirements. About 19% also identified visibility differences between LED and incandescent signals, but respondents differed about precisely which aspects of visibility differed and which were advantageous and disadvantageous for LED signals:

Possible visibility advantages

• clustered sources versus single source: if the light source in an incandescent signal burns out the entire signal is ineffective; even if many LEDs burn out a partial luminous signal is provided
• LED signals were reported by one participant as being brighter than incandescent signals; this may be an incorrect assumption if based only upon the luminous intensity requirements because LED signals might in fact have lower intensities than incandescent signals according to the interim specification of the ITE, for example
• the faster rise and decay (on and off) times possible with LEDs was identified as a possible visibility advantage because more rapid changes in the visual environment tend to be more conspicuous than slower changes

Possible visibility disadvantages

• the narrow distribution of LEDs was identified as a possible disadvantage if the signal does not provide the required intensity distribution
• the potential for luminous degradation of LEDs throughout the life of a signal was also identified as a potential disadvantage
• questions about the relative equivalence in color of LED and incandescent signals were also identified as a possible disadvantage

A separate question specifically asked participants to compare the visibility provided by LED and incandescent signals. About 48% stated that LED and incandescent signals were equally visible and 45% stated that LED signals offered superior visibility. However, of this 45%, 14% did identify particular visibility issues where LEDs might be at a disadvantage, including the directionality of LEDs, degradation of output over their life, and possible reductions in visibility by color-deficient drivers.

Physical differences between LED and incandescent were also identified by 6% of survey respondents. It was noted (incorrectly) that LED signals are larger than incandescent signals and (correctly) that since LED signals also contain many additional electronic components in addition to the light sources, they could be more susceptible to certain kinds of damage, particularly electrical damage.

Survey participants were also asked about their perceptions about the relative performance of LED traffic signals in different weather conditions. Half (50%) of the respondents to this question stated that there were no differences between the performance of LED and incandescent traffic signals in different weather conditions. About 27% noted that LEDs have potential to produce lower output in higher temperatures (and in some cases, higher output in colder temperatures), and 7% stated that LED signals have better "fog penetrating" characteristics but did not specify why. About 17% were not aware of weather-dependent differences between LED and incandescent signals.

Comparison among different colored LED signals

Participants were also asked to identify any differences that might exist among the different colors of LED signals. About 33% of the respondents to this question identified cost differences between red and green signals, with green ones being more expensive. Similarly, an additional 30% stated that technological differences existed among red, yellow and green signals. While most participants seemed to be aware that certain cost and technology differences exist, few articulated what those specific differences were except in very general terms. About 15% of the survey respondents reported no major differences among any of the colored LED signals, while 22% did not know. Specific information about the different technologies in colored LED signals and their impact on market factors appears to be lacking among respondents.

Comparison among LED signal installation types

One survey question asked participants how well LED traffic signals would perform with different types of installation. About 65% stated that LED signals work equally well regardless of the type of installation, but 23% stated that pole-mounted installations were preferable for LED signals because in span wire (suspended) installations, the signal is more susceptible to being turned by wind and because the directionality of LEDs might compromise the visibility of LED signals in these conditions. In addition, 13% were not aware of the impact of installation type on LED signal performance.

1. Survey Questionnaire
2. List of Municipalities Surveyed
3. Market Snapshot
4. Specification and Purchasing
5. Technical Issues
6. Potential Market Activities
7. Summary and Conclusion