Paper, 'On a new standard of illumination and the measurement of light' by W H [William Henry] Preece

Description

Preece writes: ' The present position of photometry as practically applied to electric lighting is by no means in a satisfactory condition. Mathematical accuracy in the measurement of the intensity of the light emitted by a given source is unobtainable owing to the numerous disturbing influences of quality and quantity which render impossible any graduated scale of light. An absolute standard of light has not yet been obtained. I have long felt that to meet the case of electric light illumination we must not depend upon any direct comparison between the light, emitted by the source to be measured and any given recognised standard of light; but that we should rather make our standard of comparison an area illuminated to a given intensity whatever be the source of light. We do not want to know so much the intensity of the light emitted by a lamp, as the intensity of illumination of the surface of the book we are reading, or of the paper on which we are writing, or of the walls upon which we hang our pictures, or of the surface of the streets and of the pavements upon which the busy traffic of cities circulates. Illumination of this character depends not on one source only, but on many sources of light distributed in innumerable ways. Hence, I propose to measure the illumination of surfaces quite independent of the sources of light by which they are illuminated. The difficulties in comparing the illumination of spaces have hitherto been insurmountable, but now, thanks to the beautiful little glow lamps introduced by Mr Swan, these difficulties have disappeared. The standard I propose is the space illuminated by 1 British standard candle at 12.7 inches distance, which is the same as the illumination given by 1 French standard “bec” on the same space at 1 metre distance.'

Annotations in pencil and ink throughout. Includes two diagrams of experimental apparatus.

Subject: Optics

Received and read 21 June 1883.

A version of this paper was published in volume 36 of the Proceedings of the Royal Society as 'On a new standard of illumination and the measurement of light'.

Reference number

PP/4/24

Earliest possible date

1883

Physical description

Ink and graphite pencil on paper

Page extent

12 pages

Format

Manuscript
Diagram