Do Blu-ray discs work in normal DVD players? — Vignesh, Tiruchengode, India
No, you cannot play Blu-ray discs in normal DVD players. A Blu-ray disc uses the same idea as that used in a CD and a DVD, but it has much smaller features that make it impossible for a normal DVD player to read it. A Blu-ray reader needs to use a blue LED to read such small features (hence the name), while a normal DVD drive uses a red LED.
It can go the other way however. Most Blu-ray drives can handle DVDs.
This HD video (you have to click on the HD button to see it) can help you to see the difference between DVD and Blu-ray videos. The majority of human beings seem to have decided that the difference seen here is not big enough to justify the higher price of Blu-ray discs.
For more info see: How Blu-ray Discs Work