Force and motion
Force and Motion
Sources of Infrared
The diagram above shows an IR receiver exposed to various sources of infrared light. The receiver will be activated by any source of infrared light, and any light source that also produces warmth is a source of inrafred. Therefore the sun, an incandescent bulb or an electric space heater should all trigger the IR receiver. When exposing the receiver to the sun, it may be hard to tell if the LED is on or not, because of the sun’s glare. To get around this problem, you can either shield LED from direc sunlight, or use a buzzer instead of an LED in the receiver circuit.
Why does an incandescent light turns on the receiver, while a fluorescent light or LED doesn’t? The answer also explains why fluorescent lights and LEDs are so much more energy efficient than conventional light bulbs. An ordinary light bulb operates at a very high temperature, and most of the energy it produces is infrared range, and therefore not visible. The purpose of a light bulb is to produce light, not heat, and from the point of view of lighting, the infrared light represents wasted energy. A fluorescent light or LED, on the other hand, produces almost entirely visible light, so much less of the energy is wasted.
If you expose the IR receiver to a TV or DVD remote controller, and press the buttons, the receiver may appear to flicker. That is because the remote does not stay on continuously, but instead produces a series of pulses, which are the code for changing the channel or volume, etc.
How come the IR receiver is black? The black surface is actually an IR filter, which lets infrared light through, but blocks visible light. If the filter weren’t there, the receiver would be triggered by visible lgiht as well as infrared, and would not be usable, except in the dark!