Flashing light

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A flashing light is a light source that changes its brightness periodically through a technical device .

use

Flashing lights are used

  • to signal different states (of devices), for example when a function is being carried out without the user being able to recognize it in any other way (e.g. reading in CD, saving digital photo on memory card, active alarm system in the car),
  • to save energy by stopping the display,
  • because flashing stimuli (just like movements) are more easily perceived than those that do not change / move (e.g. direction indicators ),
  • to divide a movement into individual images (e.g. stroboscope ).

Flashing frequency

In communication theory , the effects of different blink frequencies on people have been studied. According to these studies, humans assign different meanings and attention to different blinking frequencies . So low frequencies have a calming effect and symbolize a normal state , while high frequencies are more a warning! express. Flashing at a frequency of 1 to 2 Hz (once or twice per second) and a pulse ratio of 1: 1 (the signal is on for as long as it is off) is most noticeable . For example, StVZO § 53a, Paragraph 4, 2nd point, stipulates that a hazard warning light must flash at a frequency of 1.5 ± 0.5 Hz.

High flashing frequencies can trigger attacks of reflex epilepsy in appropriately predisposed people . Therefore, computer games with fast picture changes have warnings about this.

Types of flashing lights

Rotating screens, reflectors

The light source itself shines continuously, a screen rotates around it, which covers the light in one (or more) direction (s). For an unmoving observer, the blinking effect arises from the fact that the reflector regularly covers the light emitted in its direction. As a rule, the screen is designed as a reflector . This gives a light beam of higher light density. The flashing lights on alarm systems, on police, ambulance and special vehicles as well as in discotheques often work in this way.

Rotating lenses can be used instead of a reflector . These bundle the light in one direction so that rays with a long range are created. This technique is used in lighthouses .

In film projectors , a rotating screen rotates between the lamp and the film. It is synchronized with the film transport and interrupts the light beam when the film is advanced one frame. This allows you to see still single images in quick succession. Due to the high frequency , the blinking is not noticed and the images appear to be moving. In film cameras, the rotating diaphragm is used accordingly during exposure so that the film is only exposed in a stationary position and not during further transport.

Flashing circuits

A light source is switched on and off by electronic or electromechanical circuits. In the past, a circuit with a relay and a capacitor was used in the car blinker ; today, astable multivibrators are used . In these circuits, feedback transistors replace the relay. Both variants have in common that the flashing duration depends on the charging time of the capacitor. Flashing circuits with a high flashing frequency are called stroboscopes . They are used to break down movements into a sequence of standing individual images. There are LEDs in which a flashing circuit is already integrated. This is attached to the component as an SMD element.

Flashing lights

In flashing lamps, a bimetal switch is built into the lamp. When the heat of the filament has reached a certain temperature, the switch opens and cuts the power to the wire, so that it cools down. If the temperature falls below a lower limit, the switch closes the circuit and the process starts again.