Editing Light-emitting diode (section)

===Light properties===
* Switch on time: LEDs light up extremely quickly. A typical red indicator LED achieves full brightness in under a [[microsecond]].<ref>{{cite web|url=http://www.avagotech.com/docs/AV02-1555EN|title=Data Sheet&nbsp;— HLMP-1301, T-1 (3 mm) Diffused LED Lamps |publisher=Avago Technologies |access-date=May 30, 2010}}</ref> LEDs used in communications devices can have even faster response times.
* Focus: The solid package of the LED can be designed to [[focus (optics)|focus]] its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages [[total internal reflection]] (TIR) lenses are often used to the same effect. When large quantities of light are needed, many light sources such as LED chips are usually deployed, which are difficult to focus or [[collimate]] on the same target.
* Area light source: Single LEDs do not approximate a [[point source]] of light giving a spherical light distribution, but rather a [[Lambert's cosine law|lambertian]] distribution. So, LEDs are difficult to apply to uses needing a spherical light field. Different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees.<ref>{{Cite book|author=Hecht, E. |title=Optics|url=https://archive.org/details/optics00ehec |url-access=limited |edition=4|page=[https://archive.org/details/optics00ehec/page/n596 591]|publisher=Addison Wesley|year= 2002|isbn=978-0-19-510818-7}}</ref>