Many thanks to all who responded here or by email to my request for information on the use of a Weston Master III light meter to determine the light intensity in foot-candles shining on plants in a greenhouse. All of you gave good information on using camera light meters, but special thanks to Viateur who knew the unique simplicity of the Weston meter in making the determination. The Weston meter reads a numeric value that he understood requires only that you take a reading from a white sheet of paper held over the plants and then multiply the reading by four(4) for an approximation of the intensity of the light reaching the plants in foot-candles. This eliminates the need for setting the ASA film speed, determining the shutter speed and f/stop, and then using a chart as is required with most camera light meters. Deep in my memory, I thought the multiplying factor was four but I was uncertain. I have been slow to reply as I have been out of town. Thanks again Viateur.
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