‘Blue’ photons are energetically expensive to produce, so the most energy-efficient lamps contain the least amount of blue light. ‘Blue’ photons are not used as efficiently in photosynthesis as ‘red’ photons, but blue light has dramatic effects on plant growth. We studied the growth and development of soybean, wheat, and lettuce plants under high pressure sodium and metal halide lamps with yellow filters creating 5 fractions of blue light (< 0.1%, 2%, 6%, 12%, and 26%) at 200 and 500 μmol m-2 s-1 PPF. The response of dry mass, stem length, leaf area, SLA, and tillering/branching to blue light was species dependent. Blue light fraction determined the stem elongation response in soybean, whereas the absolute amount of blue light determined the stem elongation response in lettuce. Lettuce was highly sensitive to blue light fraction between 0% and 6% blue, but results were complicated by sensitivity to lamp type. For the parameters we studied, wheat did not respond to blue light. Soybean stem length decreased with increasing blue light fraction and leaf area was greatest at 6% blue, but total dry mass was unchanged. The data suggest that lettuce growth and development requires some added blue light, but soybean and wheat may not.