High-power light-emitting diodes (LEDs) first became commercially available in the beginning of this century. As their efficiency and light yield improved, LEDs began to be used in applications that previously were restricted to conventional filament, halogen or discharge lamps.
 
In medical as well as industrial applications, cold-light sources are often used for illumination. Microscopy and endoscopy are two examples. Halogen or xenon lamps combined with appropriate spectral filters typically serve as the light sources. LED technology has not been widely used, despite the fact that it it offers some clear advantages compared with conventional light sources. The benefits of LED technology include:
 

• No need for filtering because the emitter spectrum is inherently cold.
• A long emitter life and maintenance-free operation.
• Energy efficiency and cost effectiveness.
• A luminous flux and colour temperature comparable to or better than conventional sources.
• The adaptability of spectral characteristics to specific needs by choosing an appropriate emitter.

 
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