Dr Leonard Levy’s Pastilles Radiometer for measurement of dosage/exposure.

Radiometers are used to test for exposure to radiation. In this object exposure to X-rays. A single dot was laced on a piece of lead, or pastille holder, and then placed in a darkened area between the patient and the X-ray tube. A colour change from yellow to orange signalled that the maximum exposure had been reached without causing skin redness.

Dr Leonard Levy (1885-1971) was a researcher interested in x-rays and the use of phosphors, including for colour television. He set up a company with long-time collaborator, Donald West, known as Levy and West to produce screens for imaging and viewing purposes.

A memorial prize in Leonard’s name was established by his family, Levy Hill laboratories and the British Institute for Radiology, for the best work in the subject by someone under 40 years of age.