title: Importance of 'blue' photon levels for lettuce seedlings grown under red-light-emitting diodes.
abstract: 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 approximately 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 micromoles 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.
authors.affiliation: Department of Horticulture, University of Wisconsin, Madison 53706.
authors.forename: M E
authors.initials: ME
authors.lastname: Hoenecke
authors.forename: R J
authors.initials: RJ
authors.lastname: Bula
authors.forename: T W
authors.initials: TW
authors.lastname: Tibbitts
mesh_terms: D018548:Cotyledon / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D004780:Environment, Controlled; D018546:Hypocotyl / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D018545:Lactuca / Q000254:growth & development* / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D017785:Photons; D010788:Photosynthesis