LED Street Light Research Project

During this measure, the luminance photometer is positioned on
a tripod at the standing eye level, with the operator pointing the
photometer at the area of interest on the street or on the light
source.
On most street lighting projects, there is just one type of measurement
performance, that of illuminance in footcandles. On this
research project, the measurement was enhanced by use of two
types of luminance measurement: spot photometry and imaging
photometry. These newer technologies were the foundation
behind the most important findings of these measurements.
[Make reference to existing guides or standards for measurement.
i.e. ASSIST: Alliance for Solid-State Illumination Systems and
Technologies: A Method for Estimating Discomfort Glare from
Exterior Lighting Systems and Recommendations for Evaluating
Street and Roadway Luminaires.]
Approaches to Evaluating Public Preferences for
Streetlights
Orfield Labs surveyed a series of LED projects around the United
States and Canada. Typically, each project was predicated not on
lighting quality but on energy savings and incentives. In order to
achieve public buy-in on each project, a demonstration was generally
installed next to existing lighting, placing a new LED luminaire
next to an old high-pressure sodium HID luminaire. The public was
surveyed about the lighting to determine which they preferred.
Preference was generally in favor of the LED, as it is a much whiter
light and renders colors more accurately. Lighting levels were also
measured to ensure that both lights complied with the standards
in place. The problem with this typical evaluation is multiple levels
of bias, including surveyor shared information about LED efficiency
and LED quality.
September 2011
A more realistic comparison demonstration would have been to
put the LED luminaire next to a metal halide HID. In many cases,
the HID would have been preferred because it has lower levels of
glare, but still renders colors accurately. Secondly, it is well know
in research circles (cognitive psychology and academic market
research) that accurate subjective testing must be indirect and
must not be based on opinions. What must be measured are
the feelings and associations of the public, not their opinions, as
opinion- based research has little predictive value.
Comparisons of lighting can be done validly by using either real
street scenes or images of those scenes. But the public ranking
should be based on semantic ranking of the ‘street scene’, not the
light, and the rankings should be based on semantics that describe
important positive and negative feelings when on the streets at
night. And nothing should be shared with the public about bias
for LED, about ‘old vs. new’ lighting, etc. This type of subjective
testing is technically called Perceptual Market Research. TM
Measurements should also include lighting levels as well as luminance
and glare, which are strong determinants of use preference.
Pittsburgh LED Street Light Research Project 79