Force and motion
Force and Motion
Detecting that transmitter is on
When it is turned on, the transmitter produces a faint red glow, which not too hard to see in the dark. The reason you can see anything at all is that a little bit of the light from the transmitter is in the visible range. However, most of the light is in the infrared range, which is not visible to humans.
Even though the light from the transmitter seems very dim to us, it looks very bright to a cell phone camera. To see this, turn the transmitter on and shine it directly into the lens of the cell phone. You will see a bright light in the camera. A camera should not really see things that we can’t, but the cheap camera in a cell phone doesn’t have the filters that a more expensive camera would have.
Could our IR transmitter control a TV or DVD player? The IR transmitter might have some effect, such as turning a TV or DVD player on, but it would not be able to perform more commplex functions, such as changing the channel or volume reliably. The IR transmitter produces a steady light beam, while a TV or DVD remote encodes the information about volume and channel in a series of very rapid pulses. These pulses explain the flickering of the IR receiver when exposed to a TV or DVD remote.