The various lighting systems used for studies of plant growth in controlled environment systems differ markedly in the proportions of blue and red waveband light emitted in the visible spectrum depending both on the types of lamp chosen and on the proportions of each lamp type used. A series of new high intensity lamp systems, which provided wide variations in blue/red waveband ratios were used in these studies to test at different irradiance levels, the effects of these different light spectra on the growth of four plant species ( Sorghum bicolor L., Glycine max L., Lolium perenne L., and Trifolium repens L.). The biased spectral treatments used, resulted in marked differences in dry-matter accumulation, affected the relative proportions of leaves and stems and influenced tiller and secondary stem development. For example, final shoot dry-weight and plant height were increased approximately two-fold and leaf area was increased by 46% with sorghum under the red-biased compared with blue-biased conditions at the low irradiance level tested. Blue-biased conditions also enhanced the concentrations of amino acids (particularly aspartic and glutamic acids) and protein whereas, in contrast, red-biased sources increased the concentrations of soluble sugars and starch in the leaf tissue. The implications of these results to controlled environment studies are discussed.