Many years ago, there was a simple method to determine light intensity in foot-candles for plants in different greenhouse locations, using a Weston Master III light meter. Oldsters (like me) remember when these light meters were a mainstay in camera bags before cameras with built in light meters. Does anyone remember the simple formula for converting the numeric reading of the Weston meter to obtain an estimate of the foot-candles of light reaching the plants? As I remember, the method for greenhouses involved holding a sheet of white paper over the plants, taking a reflected light reading off the paper, then multiplying the numeric reading from the meter by a factor of ?? to give a good estimate of the foot-candles of light the plants were receiving. The method had the advantage of using a reflected light reading meter rather than requiring a direct light reading meter that was pointed toward the light source. The numeric scale on the Master III meter avoided having to use the ASA film speed, shutter speed, and f-stop to make a complicated conversion to foot-candles required when using most of the other brands of camera light meters. I used the method long ago when I built my first glass greenhouse. With time and experience, I knew which plants would receive the appropriate amount of light in various locations. Now, with a newly constructed greenhouse using a twin-wall polycarbonate cover, I have no idea what the light levels are. My old light meter still functions perfectly but I do not remember the formula. If anyone can refresh my memory on the procedure, it will be very much appreciated. Thank you in advance.
************************************** See what's free at http://www.aol.com. _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
