Students can test the growth of a variety of plants using various wavelengths of light. Norman Lamps sells inexpensive colored LED bulbs that emit the following wavelengths in nm: green (550), purple (443), pink (632), orange (560), amber (572), red (680) and blue (470). We tested growth in height, number of leaves, leaf area (using Image J), fresh weight, and dry weight of lima bean plants grown under purple, amber, blue, and pink lights, compared to controls grown under natural or white light. Initial experiments have revealed that plants grow well when placed under the following lights (6 plants under each wavelength): pink (632 nm), purple (443 nm), blue (470 nm), and amber (560 nm). Plants grown under purple, amber, and pink lights produced the greatest number of leaves (30) versus 10 for the blue and 20 for the red wavelengths. The control produced 28 leaves. However, even though plants grown in blue and red light produced fewer leaves, all plants produced around the same total leaf surface area, which means that plants grown under the blue and red lights had larger leaves. This indicates a difference in resource allocation for the plants. In the future, we will add stem diameter to our measurements.
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