A Simple Automatic Short Photoperiod Device.

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Abstract
A simplified elevator-type dark box for providing automatic short photoperiod control over greenhouse benches is described in detail. The circuit uses an R-I type motor and is somewhat simpler than that earlier described by Kramer. A still simpler circuit, which could be employed if a capacitor motor were used to raise and lower the dark box, is also described and illustrated. Each of the 2 compartments of the dark box contains an electric lamp socket, permitting interruption of the dark period in either compartment or both if desired.

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