Abstract

In studies involving the performance of operators of radar indicators it became necessary to provide data concerning the transient light patterns generated on the screens of cathode-ray tubes. This paper describes a photometer which permits the determination of brightness at any instant at a selected point on the radar screen.

A 931-A photo-multiplier tube combined with suitable optical and electronic auxiliaries provides a photometer that will respond faithfully to rapid light transients for peak brightness determinations, and will also provide data for slow brightness changes associated with phosphor decay characteristics.

The photometer described is useful down to 0.005 footlamberts when examining a circular area 0.025 inch in diameter. It will measure much greater brightness levels by incorporated sensitivity controls. Its usefulness is not limited to radar screen measurements but it is applicable to many photometric problems.

© 1948 Optical Society of America

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Figures (10)

Fig. 1
Fig. 1

Adjustment of the photometer’s spectral characteristic to simulate the human visibility function.

Fig. 2
Fig. 2

Regulated high voltage power supply.

Fig. 3
Fig. 3

Details of the photometer head.

Fig. 4
Fig. 4

Schematic of the photo-multiplier (a), load circuit for high speed phenomena (b), load circuit for low speed phenomena (c).

Fig. 5
Fig. 5

Functional plan of equipment for recording slow speed phenomena.

Fig. 6
Fig. 6

Schematic of control box.

Fig. 7
Fig. 7

Schematic of d.c. amplifier and sweep generator.

Fig. 8
Fig. 8

Schematic of relay unit.

Fig. 9
Fig. 9

Peak brightness of a radar P.P.I. sweep over a normal range of indicator tube bias values.

Fig. 10
Fig. 10

Family of brightness rise and decay functions determined at a single location on an operating radar plan position indicator.