This seminar takes you on a journey, tracing the history of a somewhat serendipitous finding in the laboratory, to the translation of this finding to the clinic and its use on patients. The journey starts with a discussion over a cup of coffee between two old friends. They devised an experiment using a photobiomodulation device, one that delivered red to near-infrared light, on a few spare parkinsonian mice left over from other experiments. The thinking was that because photobiomodulation stimulates mitochondrial function, it may improve the mitochondrial dysfunction and protect neurones against the parkinsonian insult. After a week or so, it turned out that these photobiomodulation-treated mice had more surviving neurones than those that were not treated; in addition, they were found to have improved locomotor behaviour. This led to explorations in non-human primates, the gold-standard of all animal models of the disease. Here, in this species, the same beneficial outcomes were found, namely, less pathology and improved clinical signs. These experimental findings led to clinical interest and, as it stand now, clinical trials are underway testing the efficacy of several photobiomoduation approaches in Parkinson's disease patients. There are also encouraging, early indications that photobiomodulation is effective in Alzheimer's disease, with both neuroprotective and positive cognitive behavioural outcomes being evident in mouse models of the disease. We are in the process of starting a new series of studies that test the efficacy of photobiomodulation in Alzheimer's disease further, in both animal models and in patients.