Wait, sorry. There are two books with similar titles. "The Light of Other Days" is by Stephen Baxter and Arthur C. Clarke. "Light of Other Days" is indeed by

Wait, sorry. There are two books with similar titles. "The Light of Other Days" is by Stephen Baxter and Arthur C. Clarke. "Light of Other Days" is indeed by Bob Shaw. I have not read the latter. The former deals with a new technology which allows people to see in to the past via microscopic "wormholes".