A history of light and colour measurement : science in the shadows

Judging the brightness and colour of light has long been contentious.

Alternately described as "impossible" and "routine", it was beset by problems both technical and social.

How trustworthy could such measurements be? Was the "best" standard of intensity a gas lamp, an incandescent bulb or a glowing pool of molten metal? And how much did the answers depend on the background of the specialist?

Attracting scientists, engineers, industrialists and artists, the developing subject produced a new breed of practitioner having mixed provenance.

The new measurers of light had to decide the shape not only of their specialism but of their careers: were they to be a part of physics, engineering or psychology?

The physical scientists who dominated the subject into the early 20th century made their central aim the replacement of the "problematic" human eye with physical detectors of light.

For psychologists between the wars, though, describing the complexity of colour was more important that quantifying a handful of its dimensions. And after WWII, military designers shaped the subject of radiometry and subsumed photometry and colorimetry within it.Never attaining a professional cachet, these various specialists moved fluidly between science and technology; through government, industry and administration.

This is a history of the hidden workings of physical science - a technical endeavour embedded in a social context.

It argues that this "undisciplined" subject, straddling academia, commerce and regulation, may be typical not only of 20th century science, but of its future.