Riad Saraiji

Dominant contrast as a metric for the lighting of pedestrians

CIE Publication 115 and ANSI/IESNA Recommended Practice 8-00 both use vertical illuminance 1.5 m above the ground as a design criterion for the lighting of pedestrians. While vertical illuminance has the advantage of being easy to calculate and measure, visibility is based primarily on target contrast. A central question related to the visibility of pedestrians is whether drivers need to see the whole pedestrian or can they infer the presence of a pedestrian by recognizing any part of the pedestrian’s shape. The objective of this work was to first explore various pedestrian contrast profiles that could exist and then to find a simplified approach to characterize pedestrian night-time visibility. The problem was addressed through theoretical analyses and computer simulations. Pedestrian contrast was found to be bipolar and dynamic. From the contrast profiles, we developed the concept of dominant contrast, which is defined as the contrast of any part of the pedestrian that provides the highest visibility. Dominant contrast was examined as a metric for street lighting design and night time visibility for (a) an unlit street with car headlights, (b) a lit street without car headlights and (c) a lit street with car headlights. Dominant contrast was found to be a viable metric for street lighting design and night time visibility studies.

Pedestrian visibility at night: The effect of solid state streetlights:

This study examines the effect of different types of lamps on pedestrian night time visibility. Detection distance was used as a measure of visibility. The detection distance was measured in the presence and in the absence of on-coming car headlamps in an unlit street. Subsequently, the street was lit using metal halide, high-pressure sodium or LED luminaires. A pedestrian who changed his clothing colour randomly was used as a target. The results showed that the detection distance on the unlit road was 52% shorter in the presence of on coming car headlamps than when the oncoming car headlamps were off. A person wearing black clothing was harder to see and their mean detection distance was 60% less than when the observer was not dazzled by the oncoming car headlights. When the street was lit, the detection distance was doubled. The mean detection distance using LED lamps was statistically similar to that obtained using metal halide lamps, both of which were better than the detection distance obtained under high pressure sodium lighting.

Vertical Illuminance Based Crosswalk Illumination

Abstract Current IES standards refer to pedestrian lighting in terms of minimum vertical illuminance 1.5 m above pavement level. Analysis is made to find the vertical illuminance 1.5m above pavement level facing oncoming traffic for typical street lighting configurations. Three types of calculation grids were used to simulate pedestrians on the side walk, on the street and on the median. Streets with and without median are studied with various streetlighting layouts such as staggered, and along both sides of the street. It was found that in most cases the vertical illuminance on a two way street peaks on one side of the street while, it is minimal on the other side of the street at the same lateral axis. Plan diagrams of streets showing the locations of vertical illuminance greater than 1 foot-candle and less than 0.2 foot-candle are presented.

Illuminance Degradation of LED Streetlighting Luminaires in a Hot Environment

Abstract Two LED streetlighting luminaires were installed in the city of Al-Ain, United Arab Emirates, one of the hottest regions in the world. The street was closed to traffic and illuminance measurements were taken daily every 10 minutes for 300 days including the summer of 2010. Temperature and relative humidity values were acquired inside the driver compartment of the luminaires and outside of the luminaires. This paper reports the illuminance levels, temperature, and relative humidity data. Illuminance did not change by more than 12 percent throughout the test period. The drop in illuminance was 4.5 percent per 10 degree C for the ambient temperature range of 20–40 degrees C.

A Methodology for Locating the Maximum Vertical Illuminance in Street Lighting

Abstract Current IESNA recommended practice refers to pedestrian illumination on roadways as a function of the minimum vertical illuminance Ev(min). In this article, a method is developed to find the location of the maximum Ev(min) along streets. Calculation grids are set on the side walk, along the streets and, along the median. It was found that while the vertical illuminance at one point along the street may be greater than 1 FC, at other points along the longitudinal and lateral axes, the vertical illuminance can be zero even on streets that meet the recommended horizontal illuminance targets.