Only last week I was showing my class a sodium vapour lamp and saying that there were no longer lamps like that anymore. They still exist at the end of Borrowdale. Yellow light is a mixture of red and green, so let's approximate for orange. According to the theory, red objects should reflect the red in the light but absorb the green so they should still look red. However, a blue object would absorb both red and green, thus appearing black. This is what the text books say but I am never convinced.
