Development of a more effective radiation source for use in plant-growing facilities would be of significant benefit for both research and commercial crop production applications. An array of light-emitting diodes (LEDs) that produce red radiation, supplemented with a photosynthetic photon flux (PPF) of 30 µmol·s -1 ·m -2 in the 400-to 500-nm spectral range from blue fluorescent lamps, was used effectively as a radiation source for growing plants. Growth of lettuce (Lactuca sativa L. 'Grand Rapids') plants maintained under the LED irradiation system at a total PPF of 325 µmol·s -1 ·m -2 for 21 days was equivalent to that reported in the literature for plants grown for the same time under cool-white fluorescent and incandescent radiation sources. Characteristics of the plants, such as leaf shape, color, and texture, were not different from those found with plants grown under cool-white fluorescent lamps. Estimations of the electrical energy conversion efficiency of a LED system for plant irradiation suggest that it may be as much as twice that published for fluorescent systems.

Light-emitting diodes (LEDs) with high-intensity output are being studied as a photosynthetic light source for plants. High-output LEDs have peak emission at ≈660 nm concentrated in a waveband of ±30 nm. Lettuce (Lactuca sativa `Grand Rapids') seedlings developed extended hypocotyls and elongated cotyledons when grown under these LEDs as a sole source of irradiance. This extension and elongation was prevented when the red LED radiation was supplemented with more than 15 μmol·m-2·s-1 of 400- to 500-nm photons from blue fluorescent lamps. Blue radiation effects were independent of the photon level of the red radiation.

A simple, rapid procedure is described for evaluating ozone injury to leaves of Phaseolus vulgaris L. cv. Pinto. Leaf chlorophyl is extracted with ethanol and analyzed spectrophotometncally; the concentration is expressed on the basis of leaf dry weight.The per cent chlorophyll reduction of ozone-injured leaves was highly correlated with the per cent visible necrosis and chlorosis (r = 0.96). The variability in injury estimates with chlorophyll analysis was slightly less than with visual evaluation. An evaluation of chlorophyll a and b concentrations separately showed that the chlorophyUl a/b ratio decreased with increasing amounts of injury. Chlorophyll determinations made for leaves harvested at intervals after an ozone treatment indicated that maximum chlorophyll reduction had occurred by 4 days. This procedure for measuring ozone injury should be useful in eliminating the human bias associated with visible estimates of injury.

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