Is it a particle? Or is it a wave? This week we're looking at light. From its earliest origins and what it can reveal about the Big Bang, to why Newton prodded his eye with a needle to probe the origins of colour, how the brain decodes the visual world and bionic implants to reverse blindness. Plus, in the news, a revelation in the remarkable colour-changing capabilities of chameleons, how an ultrasound can combat Alzheimer's Disease, and what people do with their fingers following a handshake...