Figure 1. Incandescent lamps (INC) promote stem elongation more than other common greenhouse lamps, including cool-white fluorescent (CWF), high-pressure sodium (HPS), and metal halide (MH). Photo courtesy of Cathy Whitman.

Figure 2. Left to right: plants were grown under a DIF of +18 °F, +9 °F, 0 °F, or a −9 °F. Plants are generally shorter at flower when the night temperature increases relative to the day temperature.