First, a prism splits the light into its constituent colours, using a prism or diffraction grating, creating a spectrum. Then a camera detects the amounts of each colour of light.

Finally, a computer uses this colour information to calculate changes in the way that certain parts of the brain are using oxygen and generating energy, giving a readout of brain metabolism and activity. It’s completely harmless and non-invasive – just like shining a torch against your skin.

Certain molecules in the brain – such as oxygen-carrying chemicals in the blood and cytochrome c oxidase in mitochondria – change colour depending on their activity and oxygen levels. Different colour molecules absorb and reflect different colours of light, so by measuring the colours of the light that passes through the brain, we can work out the amounts and activity of these molecules.

Here’s one of our machines that we have built in the lab. It’s now being used by our team of doctors and engineers to monitor newborn babies in the neonatal intensive care unit at UCL Hospital.