able to overpower ambient lighting and make stop-motion effects apparent without the need for dark ambient operating conditions. They are also used as measuring instruments for determining cyclic speed. As a timing light they are used to set the ignition timing of internal combustion engines. In medicine, stroboscopes are used to view the vocal cords for the diagnosis of conditions that have produced dysphonia (hoarseness). The patient hums or speaks into a microphone which in turn activates the stroboscope at either the same or a slightly different frequency. The light source and a camera are positioned by endoscopy. Another application of the stroboscope can be seen on many gramophone turntables. The edge of the platter has marks at specific intervals so that when viewed under fluorescent lighting powered at mains frequency, provided the platter is rotating at the correct speed, the marks appear to be stationary. This will not work well under incandescent lighting, as incandescent bulbs don't significantly strobe. For this reason, some turntables have a neon bulb or LED next to the platter. The LED must be driven by a half wave rectifier from the mains transformer, or by an oscillator. Flashing lamp strobes are also adapted for pop use, as a lighting effect for discotheques and night clubs where they give the impression of dancing in slow motion. The strobe rate of these devices is typically not very precise or very fast, because the entertainment application does not usually require a high degree of performance. Fechner color Rapid flashing of the stroboscopic light can give the illusion that white light is tinged with color, known as Fechner color. Within certain ranges, the apparent color can be controlled by the frequency of the flash. Effective stimuli frequencies go from 3 Hz upwards, with optimal frequencies of about 4–6 Hz. The colours are an illusion generated in the mind of the observer and not a real color. The Benham's top demonstrates the effect. See also Electrotachyscope Flip book Reciprocating motion Phenakistoscope Praxinoscope Strobe light Strobe tuner Tachometer Thaumatrope Zoetrope References External links Demonstration of Phenakistoscope and Stroboscope at North Carolina School of Science and Mathematics Audiovisual introductions in 1832 Measuring instruments Medical equipment