Red and infrared light are part of the light spectrum, found in sun and firelight. These wavelengths of light are bioactive, meaning they affect how our cells function. We know our bodies need vitamins, minerals and nutrients, but most people don't realise our cells need adequate light of specific wavelengths to stay healthy too. People who spend most of their lives inside under artificial light put themselves at risk of ill-health – it's another form of malnutrition, known as mal-illumination.