Unlike domestic disagreements over the glow of a bedside reading lamp, the surveys Mr. Thompson and others filled out consider public safety — respondents are asked to agree or disagree with statements like “It would be safe to walk here, alone, during darkness hours,” “I cannot tell the colors of things due to the lighting” and “The lighting enables safe vehicular navigation.” And their answers could affect how cities everywhere are illuminated.

Utilities want to know whether L.E.D. streetlights, tens of thousands of which have already been installed in parts of many cities, including Seattle and Los Angeles, are a promising long-term technology that could shape large government contracts. Municipalities want to be sure that the significant savings in energy and costs L.E.D.’s can provide are sustainable enough to compensate for startup costs, but also that they do not threaten public safety or urban ambience.

Seattle is the fourth city to participate in the survey, following Anchorage, San Diego and San Jose, but it is hard to imagine the others being as enthusiastic.

“The big difference is you’re talking not only about the efficiency of the change in technology, but also the quality of light,” said Scott Thomsen, a spokesman for Seattle City Light, which claims to be the nation’s first carbon-neutral utility, largely because most of its power comes from hydroelectric dams.

As surveyors strolled the sidewalk, the 15-block stretch of 15th Avenue was closed to traffic so that a test car could drive up and down at 35 miles per hour, over and over, carrying passengers who pushed buttons whenever they saw certain markers placed in the street. The passengers, like the strollers, were gauging visibility in different lighting variations. Over the course of the night, lights were dimmed to test how low they could safely go.