Editorial: The measure of light

Listening to the evening news bulletin recently, I was struck how much of the reporting could be directly linked to measurement, and how much we take for granted our ability to quantify all manner of things in a meaningful, consistent and reproducible manner. Of course, much of what we measure is relatively straightforward: counting the number of people in hospital with Covidrelated complications, or recording the warmest New Year’s Day ever in the UK, for example, can both be done without the need for complicated measurement equipment or analysis (although the latter does require good calibration of weather station thermometers). But what about more complex measurements, such as the amount of CO2 in the atmosphere? Reliable and meaningful data in these cases are only possible as a result of international collaborations to collect and process information gathered from a wide range of different sensors, all of which must be linked to a consistent set of measurement units. As our need to understand and quantify the impact of human activity on the environment increases, so too does our need for relevant and reliable systems of measurement. Light and lighting present their own measurement challenges. Those, too, are becoming more complex as our understanding of the impact of optical radiation on human health and wellbeing improves, and our desire to use the energy consumed by lighting more effectively increases. No longer is it enough to know (i.e. measure) the amount of visible light delivered for a given amount of energy. We also need to consider how that light might affect our sleep-wake cycle, our mood, our ability to concentrate and so on. Our understanding of the wide-reaching impact of optical radiation on human biology and behaviour is still in its infancy and there is much that still needs to be investigated. In parallel with better knowledge comes a desire to translate research findings into improved lighting products and practice. And that in turn means we need a measurement framework that not only allows us to collect and analyse information about the relevant properties of “lighting”, but also to communicate and quantify those properties in a meaningful and understandable way. Any such measurement system must also be compliant with the International System of Units (SI), which is essential to enable traceable measurements and the establishment of international standards and guidelines. I hope all those involved in this important area of research will continue to keep the ultimate need for a relevant and reliable measurement system in mind and continue their collaborations to achieve this goal. To quote Lord Kelvin: “When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.”