The characterisation of optical radiation detectors is important in a wide range of applications, such as environmental measurements; colour processing; food; transport; chemical and pharmaceutical industries; and the medical and communications sectors. Cryogenic radiometry, initially developed at NPL, is now widely used by most NMIs as the basis of all optical radiation scales, including the SI base unit, the candela.

As well as providing traceability via calibrated detectors, NPL also provides a wide variety of other services, ranging from measurements of important parameters such as detector linearity and uniformity, through to the design and supply of bespoke radiometric measurement facilities.

NPL is also working on the application of filter radiometry to the determination of high temperature fixed points based on eutectics and the development of improved approaches to traceability for the most demanding application areas, particularly Earth observation and climate change.