Emergency vehicles use a type of strobe light.
Strobe and flashing lights categories overlap. Many–but not all–strobe lights are also flashing lights, while some flashing lights are strobes. Strobe lights used in entertainment contexts, such as special film effects and haunted houses, are a different type of strobe from those used for emergency vehicles. To add to the confusion, nightclubs use both types of strobes.
The word “strobe” comes from the Greek “strobos,” which means “to spin” or “to whirl.” The original stroboscope, the forerunner of the modern strobe light, placed a spinning fan blade-like object in front of a light so the light only became visible when openings in the object passed in front of the beam. Rapidly blocking and unblocking the light mimics flashes on and off, but without a change in intensity. Flashing lights, in general, turn on and off due to interrupted power to the light bulb. This means the lamp’s filament must repeatedly heat and cool, leading to variations in the light intensity as it fades on and off.
Whirling vs. Flashing
Emergency vehicles use a second type of strobe. These lights have an internal mechanism that spins one or two bright lights around inside a case, which is usually tinted blue or red. As the lights spin, they shine outward through openings in a housing inside the case, creating a flashing effect. However, because the effect is created by spinning rather than powering on and off, it is technically a strobe.
Flashing lights can draw attention, such as flashing lights on signs or traffic signals, or to create a lively atmosphere due to constantly changing visuals, such as you might find in Las Vegas casinos. The visual effect commonly known as a strobe effect requires absolute darkness when the light is off or covered. The regular intervals of dark and light allow you to see images as distinct events instead of your brain interpreting them as fluid motion. This creates the stop-motion effect for which strobe lights are known.
Some forms of epilepsy make people sensitive to flashing light, so both flashes and strobes can trigger epileptic fits. This is why you may see warning signs outside nightclubs or theatrical performances that use strobe lights. Commercially available strobe lights usually flash no more than 10 to 12 times per second, which minimizes the risk of triggering seizures. However, lights that are flashed manually can be set to turn on and off at higher speeds, increasing seizure risk. Slower flashing and strobing speeds can still trigger epileptic fits in prone individuals, so use care when using any flashing or strobing light.