https://www.youtube.com/watch?v=IXxZRZxafEQ
This video from the YouTube channel 'In a Nutshell' (formerly kurz gesagt) is a great way of introducing the concept of light. It is appropriate for any student of secondary age (Year 7-13) with some very short aspects that are a too complex for younger pupils to understand but which are not integral to the video itself.
It also makes reference to the electromagnetic spectrum so could be a great way of introducing this as a topic for Key Stage 4 (GCSE) pupils.