An application of the law of intensity is made in using a simple (Bunsen) photometer.
The photometer or instrument for accurate comparison of lights, their amount and intensity, tells a different story.
A valve is then fitted to one of the front openings, so that the light in that half of the photometer may be gradually diminished.
There is no other way of measuring the exposure than by the photometer or personal experience, and the latter is by far the best.
A number of measurements of the illuminating power of an electric lamp were rapidly made during the lecture with this photometer.
The photometer, preferably one of the Lummer-Brodhun form, is set up on a gallery or bench.
The photometer may show a very adequate intensity of illumination; nevertheless seeing may be unsatisfactory or even impossible.
In such a case the photometer yielded results quite likely to be misinterpreted as satisfactory.
The photometer has played an important rôle in establishing the scientific basis of camouflage.