1. The problem statement, all variables and given/known data Hi, I have to do lab experiment - estimating infrared wavelength (from remote control). My experimental setup includes CD, remote control, webcam (without IR filter, so I can see the infrared radiation), sheet of paper (I will see diffracted light spots on it) with hole for infrared diode (opposite to the CD). I will obtain angle theta from distance between CD and diode (l) and between first order spot and hole (x). CD grooves spacing length (d) is known. So, I have no problem with theory behind this experiment. 2. Relevant equations 3. The attempt at a solution But when I tried to do that, something went wrong - independently of length between CD and sheet of paper (from a few centimeters to approx. one meter), I couldn't see the diffracted light! I could only see shining IR diode but nothing else. What I did wrong? Previously, I did similar experiment with laser pointer and everything was OK.