Incandescent lighting in many domestic and commercial applications is in the process of replacement by more efficient light sources, such as the compact fluorescent light (CFL) and the light emitting diode (LED). For household use, both CFL and LED sources have a significant blue component in the emitted spectrum in comparison to the warmer incandescent globes and this has been the cause of emerging health concerns. Recent research suggests that the blue light bandwidth in the visible spectrum has a significant impact on physical health, including disruption of the internal body clock and suppression of melatonin secretion at night. This disruptive effect has been linked to a range of illnesses, including breast cancer, prostate cancer, heart disease, obesity, and diabetes. There have also been positive effects observed, including re-setting the body clock to the required sleep pattern, boosting mood, alertness, cognitive performance, and alleviating seasonal affective depression (SAD). In this paper, an introduction and review of recent research is provided, relevant health issues are highlighted and discussed, and uncertainty analysis completed for the dose-response curve for melatonin suppression as a function of incident photon density.