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The photographic method for rècording average illuminations

Published online by Cambridge University Press:  11 May 2009

L. E. Bayliss
L. E. Bayliss
Affiliation:
Department of Physiology, University of Edinburgh, and the Marine Biological Laboratory, Plymouth
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Extract

1. The photographic neutral-tint wedge method of measuring the total illumination falling on an area over a long period of time is described.

2. A study is made of the chief sources of error inherent in photographic methods, i.e. (a) the uncertainty in the value of the wedge constant, and (b) the failure of the reciprocity law, in that the amount of blackening of the photographic emulsion is not, in general, strictly proportional to the product of the intensity of the illumination and the duration of the exposure.

3. It is shown that P.O.P. obeys the reciprocity law sufficiently closely for durations of exposure between 1 and 24 hr. Gaslight paper, on the other hand, can only be used when the duration of exposure is less than about I hr.

4. It is shown that when P.O.P. is used, and a sheet of diffusing glass is placed above the wedge, the value of the wedge constant is sensibly independent of the direction and quality of the incident light.

5. Spectral sensitivity curves to tungsten filament light for gaslight paper and P.O.P. have been evaluated. From these, and other data, correction factors have been calculated for converting the photographic measurements of illumination into visual units.

6. It is concluded that the method is sufficiently reliable for use in the field, where its simplicity and the small amount of apparatus required, make it specially suitable. The experimental uncertainty is about ±5 to ±10%.

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 23 , Issue 1 , November 1938 , pp. 99 - 118
Copyright
Copyright © Marine Biological Association of the United Kingdom 1938

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References

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