The US Department of
Energy (DOE) through its Gateway Demonstration Program has once again struck a
chord with lighting designers and manufacturers related to the development of pedestrian-friendly
outdoor lighting. I have witnessed first
hand that nighttime outdoor lighting has been designed locally for the vehicle
driver, rather than the pedestrian. This
was reaffirmed by DOE's Pacific Northwest National Laboratory in a report
issued late last year.
The Pedestrian
Friendly Outdoor Light Report noted that metrics such as pavement illuminance
or luminance, illuminance uniformity ratios, vertical illuminance on objects or
faces, and glare metrics such as Veiling Luminance Ratio or Glare Ratings from the
Illuminating Engineering Society (IES) Luminaire Classification System (BUG) guide
decision making among municipal and state governments and agencies.
The U.S. Department of Energy GATEWAY Demonstration
Program featured pedestrian-focused projects at Stanford University in California and the Chautauqua
Institution in New York. The results from these projects revealed that
pedestrians have different criteria and
priorities than drivers, especially in areas where cars are subordinate to
bicycles and users on foot. Both of the demonstration areas tested multiple
light fixtures based on LED and legacy sources in an attempt to identify
luminaires that were both safe and pleasant for the residents with minimal
glare. The results of the demonstrations showed that of the current commercial
technologies, LED luminaires can serve the communities' needs with warmer correlated
color temperatures (CCT) and glare reduction techniques, and also may change
the thinking of lighting professionals on appropriate light levels.
Also in both cases,
it became clear that users
• Cared about the
daytime appearance of the luminaire
• Found luminaire
glare to be a significant factor in luminaire acceptability
• Preferred
luminaires that produced a soft-edged pattern of light on the ground
• Preferred a warm
color of light (2700K to 3000K) given the character of their neighborhood and
the fact that they were used to either
incandescent sources or high-pressure sodium as a baseline
The work verified
that glare is a significant factor in pedestrian ratings of lighting. Indeed,
the LED products that proved most preferred were augmented with diffusers to
further soften the appearance of the lights. The test subjects also preferred a
soft-edge pattern of light on the ground, whereas streetlight projects often
seek sharp boundaries on beam patterns.
The research also
revealed that area lighting in pedestrian-centric areas could essentially offer
better nighttime visibility at the low end of IES guidelines on luminance and
illuminance. Elimination of glare, enabled in part by lower lighting levels,
allows the human visual system to better perceive objects and possible danger
in areas of lower light away from the nearest light source.
Every outdoor
lighting project is different.
The needs vary
according to the project client, the users, and their activities, and therefore
the best lighting solution will also vary from project to project. There
are invariably
trade offs that must be weighed among visual comfort, color, visibility,
efficacy, and other factors. There is no glare metric that works reliably for
pedestrian lighting, so full-scale mock ups or pilot projects are an important
step for gathering feedback from users.
DOE said "The
report is meant to stimulate discussion among specifiers,users, energy
specialists, and industry in hopes that new approaches, metrics, and standards
can be developed to support
pedestrian-focused communities, while reducing energy use."
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