Seeking a New Cost Model

24-05-2012

The Need for a Lighting Review:
ItÃ¯Â¿Â½s common practice to reduce lighting design guidelines to the quantitative call for a specific level of illuminance, and in the process lose the (often qualitative and therefore potentially complex) recommendations that lie behind the numbers, which is a pity because possibilities for improved lighting conditions and reduced costs usually rest within those recommendations.

Light Patterning
The obvious starting point for a review of this type is to interrogate this quantitative Ã¯Â¿Â½blanket designÃ¯Â¿Â½ approach. The illuminance figures stated in the SLL Guides are based on task-based criteria. But a task requiring, say, 400 Lux for its proper execution does not require the entire room to be lit to that same level. If the task is limited to one dedicated area, then the rest of the room is potentially overlit. Lighting in those parts of the room could possibly be reduced to just 50% of the Ã¯Â¿Â½designÃ¯Â¿Â½ figure.

This is a complete turn-about in lighting planning, but one that is gaining a lot of ground now that low-energy and sustainability practices is having such an impact on design thinking.

Light Control
There is a further argument that develops out of the idea of planned, task-based, illuminance; because those illuminance levels are only required when the task is being performed, we donÃ¯Â¿Â½t even need that level of light in that particular space all the time. So why not investigate light level control as well as tightening-up on the location of enhanced illuminance levels. ItÃ¯Â¿Â½s no different to switching on a table lamp so that you can read a book while the rest of the family is watching the TV.

Light Efficiency
The third strand to this type of lighting design overhaul is to look again at the technology thatÃ¯Â¿Â½s being used. The requirement for Ã¯Â¿Â½high frequency control gearÃ¯Â¿Â½ in fluorescent luminaires is a worthy statement, but it does not go far enough. All that the HF control gear requirement does is to ensure that you get a more energy-efficient lamp and gear arrangement, rather than the pre-historic switch-start, wound-ballast, version. But it says nothing about luminaire performance, which is where our attention should be aimed, because if itÃ¯Â¿Â½s a poor luminaire, then the inclusion of efficient control gear does nothing to help.

Cost Planning
A few words here about how we need to change the way that we assess project costs. The old cost comparison model is based on the Ã¯Â¿Â½blanket designÃ¯Â¿Â½ approach; we light an entire room to a particular illuminance for a particular period of time Ã¯Â¿Â½ usually the whole working day. That only requires a simple bit of mathematics to translate the physical situation into a projected kWh cost. Payback periods for better (more expensive) technology could be worked against that model, but now that weÃ¯Â¿Â½re contemplating a high energy cost future in a low-carbon environment that model no longer serves.

We need to squeeze the last drop out of the Ã¯Â¿Â½lamp+control-gear+luminaireÃ¯Â¿Â½ hardware, and that means we must ensure that weÃ¯Â¿Â½re utilizing the best that product design has to offer, and thereÃ¯Â¿Â½s a cost associated with that. But we also want to reduce the length of time that we use the hardware, and even have the facility to reduce the luminaire's output when required. That means we spend more money on our luminaire and our control arrangements and we only begin to see the savings that weÃ¯Â¿Â½re making when a proper Life Cycle Assessment is made of the installation. Arguing the low-unit-cost against the efficient-high-tech model no longer works for us, and itÃ¯Â¿Â½s going to be a bit of an adventure seeking out a new model that does work.