As we have developed the technology of lighting we have also developed our understanding of how to use light. Through standards we lay down limits for safety and adequacy, through guides we direct lighting toward established good practice, show how to transcend the adequate. We have learnt how to give light meaning, transforming spaces by giving them a lit atmosphere, applying light to give beauty to a scene.

But the use of light is constantly challenging us. It is no longer enough to ensure good task visibility, or a comfortable environment. It is not even enough to produce an environment that gives a sense of well-being. We need to do all these, but also in a way that minimises harm to the environment. Therefore stricter rules are being applied to product design, use and disposal. We have to minimise the carbon footprint of a product or an installation and maximise sustainability. Therefore, all aspects of design, whether for a luminaire or lighting installation, is a balance of factors, a balance of performance, efficiency and comfort (PEC).

Performance is the achievement of visual effectiveness, meeting requirements and targets. It is quantifiable through known lighting measures such as illuminance, luminance, glare rating, colour rendition and uniformity. These measures are generally defined through national and international standards and recommendations.

Efficiency is conserving energy and effort, reducing CO2 emissions and waste, producing a system that is practical and efficient to install, operate and maintain. Efficiency can also be quantified, through units such as lumens/watt, cost/m2, CO2 kg/year, percent recycled element, percent maintenance link, and many others. Some of these measures are defined through national and international standards and recommendations, such as energy efficiency or the ecodesign of products, whilst others are concerns for the end-user, such as cost.

Comfort is the achievement of complete satisfaction, providing a stimulating atmosphere that gives sustainable wellness. The criteria for assessing comfort are subjective and are the criteria that differentiate the design, that give the design its individuality, its own character. Is it calming/stimulating/inspiring, welcoming and pleasant, reassuring, fulfilling? Does it have a pleasing flow of light and give a well balanced ambient? Do all parts of the design complement each other, the architecture of the space, the lit effect, and the physical design of theluminaires? This is the point where the engineering and art are blended to produce good lighting.

So in their job the designer needs to know a wide selection of information and how to blend this to deliver better lighting, with better efficiency and a better environment in a sustainable manner. This is the PEC philosophy, and in this handbook we supply some of this information to help the designer in their task.