[ 2007-01-12 09:45 ]
If we are driving a car or crossing a big road, we
will stop when the traffic lights turn red. Why do we use red instead of other
As we know, scattering occurs when lights go through the air. For the same
media, if the wavelength is long, the scattering will be short. If the
wavelength is short, then the scattering will be long.
Of all of the visible lights, red has the longest wavelength about 1.7 times
that of purple, so the scattering is the weakest. That means red light travels
far. In fact, it travels farther on rainy or foggy days because of the reduced
Using red lights as a stop signal helps drivers in more remote areas see the
signal. It helps drivers slow down or brake in time. If drivers didn't see the
stop signal until they were close, they may not be able to stop the car in time,
possibly causing an accident. Red is also a color that excites people, the optic
nerve especially responds to red. In short, red lights help drivers stop in time
and help prevent accidents.
Red lights are not only used for stop signals but also warnings. For example,
red lights are installed on the tops of tall buildings in cities so that pilots
in aircraft can clearly see them at night. Red lights are also used for public
security and fire department vehicles.
（北京林业大学通讯员黄典钰供稿 英语点津 Annabel 编辑）