In his workroom in Frith Street, Baird continued his researches. These he described in a paper published in the January 1925 issue of Wireless World and Radio Review. Baird was now attempting to transmit the image of an object by reflecting light from it rather than by having a source of light behind the object. This was a problem of quite a different order of difficulty to the problem of the transmission of shadowgraphs. The latter problem requires the light cell to distinguish between total darkness on the one hand and the maximum intensity of the light source, possibly several thousand candle power, on the other hand; but in viewing an object by reflected light, the photocell has to discriminate between darkness and the very small light flux reflected from the white parts of the object. As Baird noted in his paper, 'the apparatus has therefore to be capable of detecting changes of light, probably at least a thousand times less in intensity than when shadowgraphs are being transmitted.'

Inspec keywords: television broadcasting; television production

Other keywords: Frith street; photocell; John Logie Baird; television pioneer; shadowgraph transmission

Subjects: Radio and television broadcasting