Yes, I've noticed and thought about these also
In regards to a DVD as opposed to a CD, the DVD when cut,firstly in half, actually delaminates in to TWO DISCS (dual layer)
From half of that DVD comes a thin and quite bright grating(reflective) and one clear grating..........how good it is to a CD or non delaminated DVD is not as yet known.
Initial tests easily reveal spectrra from bright street lamps and fluro house lighting..............and this is from a CD or DVD!!!
Some trivia : CD = 600+ lines per mm, DVD = 1300+ lines per mm.
Merlin66, any suggestions on which will be better - CD or DVD ?
Cheers,
Rob.