Lighting : LIGHTING-April-2017
44 LIGHTING MAGAZINE | April/May 2017 April/May 2017 | LIGHTING MAGAZINE 45 TECHNICAL FEATURE Christchurch pedestrian crossing lighting upgrade By Yunyu Zhu – Lighting Design Engineer, Connetics Ltd, NZ INTRODUCTION In July 2015, Christchurch City Council decided to carry out a lighting upgrade project, to replace the 125W mercury vapour (MV) and some 150W metal halide (MH) luminaires with new LED luminaires, at 23 pedestrian crossings. As a cost effective approach, existing columns and cable positions were to be utilised. Determining factors for the lighting upgrade were: l Safety consideration Existing MV and MH luminaires failed to achieve required pedestrian crossing lighting standards, which lead to potential risk to drivers and pedestrians using the crossing points. l Energy efficiency and maintenance consideration Existing luminaires were identified as uneconomic to operate and maintain, due to age and energy consumption, compared with more efficient LED products available and affordable in the market; also, MV lamps are becoming obsolete which makes it unable to maintain them in the future. DESIGN CRITERIA The pedestrian crossings were on Category V roads or busy Category P roads, therefore in accordance with AS/ NZS 1158, Part 4: lighting of pedestrian crossings, “X1” was selected as the applicable lighting standard for this design1. The required illuminance values are shown in Table 1 (an excerpt of table 3.5 from AS/NZS 1158, Part 4). PEDESTRIAN CROSSING LAYOUT Instead of a separate design for each crossing, the Council requested the use of three models to represent all crossings, due to the fact that all crossings fell into one of the following dimension group: 11m (length) x 5m (width) 10m (length) x 5m (width) 7m (length) x 5m (width) DESIGN ANALYSIS Illuminance calculations In order to provide a clear presentation, horizontal and vertical calculations exported from lighting design software, AGI32 (version 16.3 .13), are shown individually in the plan and side views shown in Figures 2 and 3. The values are maintained illuminances. All the values shown in Figure 2 and 3 indicate the crossing is compliant with the Standard’s requirements for Subcategory X1. Energy savings As the result of the combined lighting upgrades, a reduction in energy consumption of 55% was achieved (see Table 2). This would save 12,775 kWh of energy annually, which would add up to 255,510 kWh over twenty years’ time — the luminaire life expectancy. OTHER CONSIDERATIONS Glare control and Upward Waste Light Ratio (UWLR) As part of luminaire assessment process, glare control and UWLR were important considerations, addressed by mounting the luminaires at zero degrees and selecting luminaires with special optics designed for pedestrian crossings. Table 1. Values of light technical parameters (LTP) for New Zealand Pedestrian Crossings2 Lighting subcategory Point horizontal illuminance – Marked crossing(Eph) Point horizontal illuminance – Surrounds(Eph) Point vertical illuminance – Marked crossing(Epv) Glare control and UWLR X1 30 lux (measured on road surface) 10 lux (measured on pathway surface) 20 lux (measured 1m above road surface) See Clause 3.3.5 Figure 1. Typical pedestrian crossing layout. (Note: drawing is not to scale.) Figure 2. Within the marked crossing area (10m × 5m), all the horizontal illuminances were greater than 30 lux while within the surrounding areas (5m × 3m), all values were greater than 20 lux. Figure 3. Vertical illuminance calculations. The magenta arrow indicates calculation point direction. At each calculation point (1m above road surface) on the vertical plane (10m × 1m), all vertical illuminances were above 20 lux, with the lowest calculated value being 20.6 lux occurring at the mid-point of the crossing (furthest from the light source) which was expected.