A light-emitting diode (LED) is a solid-state light source. Introduced as a practical component in 1962, early devices emitted low-intensity red light, but modern versions are available across the visible, ultraviolet, and infra-red wavelengths now with high brightness. They are used as indicator lamps and increasingly for general lighting.



LED Timeline

  • Electro-luminescence, 1907 by Britisher H. J. Round using silicon-carbide ‘cat’s-whisker’. Yellow/Green light – 1st LED.
  • Infra-red from GaAs, 1955.
  • First practical visible spectrum (red), 1962.
  • Alphanumeric displays and handheld calculators, 1968.
  • Blue output, 1971.
  • First ‘high power’ yellow and red/red-orange devices, 1972.
  • Green light, 1974.
  • First ‘high brightness’ blue made, 1993.
  • First White units made, 1996.
  • UV and deep violet, 2001.450px-LED,_5mm,_green_(en).svg
  • White ‘high power’, 2003.



Precise clinical diagnosis needs outstanding illumination. New powerful white LEDs offer many advantages over incandescent filament bulbs that are used in most current ’non-camera’, portable, handheld or head-mounted clinical diagnostic instruments, such as direct or indirect ophthalmoscopes, retinoscopes and otoscopes.

One of the key benefits is the spectral spread of the light they emit.

The violet/blue LED reveals skin and ocular structures superbly. It is also perfect for viewing fluorescein patterns and corneal defects, skin, and even teeth. The wavelength output provides good dye fluorescence without obscuring target tissue with excessive veiling visible light.



Even when the light output is almost fully dimmed there is no colour variation – unlike a filament source which produces a distinctly orange cast. The latest generation of high-power LEDs (~2014) maintain their light output superbly over their life. Simply put – these robust light sources have:

● an ultra-long life – enabling simpler ‘one-piece’ instrument construction

● a heat-free ‘cool’ light beam – enabling safer, superior patient comfort

● a tailorable colour temperature/spectra – giving crisp whiter light and enhanced diagnosis

A more detailed article on LED Technology (and continually updated) is to be found here from the open source Wikipedia.

« Return To Articles