The effect of far-red (FR) light, given at the end of each daily white-light period, was found to be influenced by the irradiance of the white light. Increasing the white-light irradiance decreased the effect of a given FR light dose, and the interaction was found to be statistically significant. The effect of FR light on 14C translocation was measured, and the possibility that the FR may interact with the white light through its effect on translocation is discussed