Car park lighting: Metal halides vs LEDs
Metal halide has been the standard car park light source for many years, but LED technology is advancing at an unprecedented rate. So which is best for car park lighting? WE-EF LIGHTING investigates.
The P Category lighting code provides information on and the requirements for lighting outdoor public spaces in general and car parks in particular. This code has two components that form part of the Australasian Vehicular and Pedestrian lighting standard AS/NZS1158 – AS/NZS1158.3.1 and AS/NZS1158.2.1. The former is the standard itself, while the latter is the computer-based procedure for calculating the values and results. In total there are 12 categories. P11, one of the 12 categories, specifically addresses the issues relating to the lighting of car parks. Originally there was just P11; however, today it is known as P11a, with two additional levels – P11b and P11c – having been subsequently added. In simple terms, it can be said that ‘a’ is the highest, ‘b’ intermediate and ‘c’ the lowest.
Within the standard there exists a selection process that allows designers and other stakeholders to determine the appropriate level (a, b or c) by reviewing such factors as usage, night-time occupancy rates and the risk of crime. Environmental issues such as impact on neighbouring properties and sky glow also feature as considerations.
P12, the last category, is the standard for lighting disabled parking spaces. It is often neglected or ignored, but is essential to good design practice and compliance.
Light technical parameters are the values represented by the standard that lighting designers work to in establishing compliance to the code (see Table 1).
Metal halide has been the standard light source for many years, given community preference for white light in public lighting applications. These lamps operate via a gas discharge and require electrical componentry to provide stable operation when run on a normal power supply. The luminaire itself becomes home for the metal halide lamp, a reflector system and the control gear.
These products are typically referred to as area lighting luminaires and mostly are of the ‘environmental’ style – meaning there is no upward ‘spill light’. Suitably designed poles are essential and they may vary in height from five to 10 metres.
LED technology, more specifically as a light source for commercial lighting, has been with us for a few short years, yet the advances made have been at an unprecedented rate, not least of all in the outdoor lighting arena. The surprising factor has been the rate at which the cost of LED has declined relative to metal halide. Price has all but ceased to be a major reason not to use it.
The form of an LED area lighting luminaire has changed. It no longer needs to be deep. It is, however, in the performance sense that we see the most change. We will investigate what this really means further on in the article.
The car park in Diagram 1 has been created in CAD for the purposes of this comparison. Is it typical? No, it isn’t. Is it in any way unusual? Once again, no, it isn’t. Car parks come in all shapes and sizes, thus cost and results will vary from case to case. The design process is computer-based and detailed. For the real enthusiast, the data is readily available, but for the purposes of this article, we will concentrate on the results.
The results are set out in the following tables and graphs, with the results assessed in three different ways:
- compliance to the standard
- cost in terms of owning and installing the lighting hardware, and
- environmental performance in terms of running costs and the consequent impact of 20 years of operation.
The results show that both metal halides and LEDs satisfy the requirements of the standard at all three levels. LEDs, however, meet but do not significantly exceed, the requirements. This is due to the optical control of LEDS and is an important measure of the superiority of LEDs.
LED wins at all three levels. The optical control has a dramatic and obvious impact when the number of luminaires and poles is considered. Fewer products are required and less time is taken to complete the installation.
3. ENVIRONMENTAL PERFORMANCE
Again, LED wins at all three levels. The operating cost is half or less when using LEDs and the environmental cost of LEDs is half or less that of metal halides. In this study we used the latest in metal halide technology and the last generation of LEDs, we used 13 cents per kilowatt hour for the full 20-year span and we ignored maintenance, the cost of which will favour one or the other, of course, which we will leave you to ponder.