Determining the Photographic Guide Number of an LED
BCRA: British Cave Research Association
Open access under a Creative Commons CC-BY-NC licence.
White LEDs are increasingly being used as sources of illumination for cave photography, both as modelling lamps and as alternatives to flashguns. Clearly, a simple way to determine the effectiveness of such illumination - the guide number - is to calibrate the light source in a series of practical tests. However, we can also determine the guide number theoretically. David Gibson goes through the steps in this exercise, which brings together several aspects of physics and photometry that the reader may have forgotten.
This is the final version of the article. Available from BCRA via the URL in this record.
Vol. 89, pp. 13-16