Examples from the Web for actinometer
A very suitable instrument for timing the exposure of carbon tissue is Sawyer's actinometer.Photogravure|Henry R. Blaney
The actinometer indicated an exposure of thirty seconds where in good light one would be right.
It is a good plan to employ an actinometer to judge the correct exposure.Photographic Amusements, Ninth Edition|Walter E. Woodbury and Frank R. Fraprie
You may sometimes find that the actinometer indicates a very different exposure from what the eye would lead you to expect.
For judging long exposures, the use of an actinometer (issued in many inexpensive forms) is helpful.How to Observe in Archaeology|Various