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Is there a type LED with adjustable wavelength? I need a light source with variable wavelength between 400nm and 700nm

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    \$\begingroup\$ en.wikipedia.org/wiki/Monochromator \$\endgroup\$ Mar 20, 2016 at 20:29
  • \$\begingroup\$ I am working on a project and our customer asked us that. we used RGB for making different colors at first but they rejected it and said we need to do that by changing the wavelength and we need to know what exact wavelength it has at the moment. @The Photon \$\endgroup\$ Mar 21, 2016 at 6:19
  • \$\begingroup\$ Okay, what kind of project? How much power do you need? Delivered in a beam or covering a wide area or coupled into an optical fiber? \$\endgroup\$
    – The Photon
    Mar 21, 2016 at 14:58
  • \$\begingroup\$ somethings are more visible in specific color lights. it is like a scanner on different surfaces. we prefer to use a 5V power source. we don't need to cover a wide area \$\endgroup\$ Mar 27, 2016 at 8:58

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According to https://en.wikipedia.org/wiki/CIELUV#/media/File:CIE_1976_UCS.png you only need a range from about 450 to 540 nm, if you can combine with a 400nm blue and 700nm red (at least if the light is being viewed directly rather than reflected).

Certain types of solid-state lasers have a wavelength that is modulated by a control current, but maybe by 5% (some tens of nm) not almost 2:1.

You can adjust the wavelength of an LED by changing the temperature, for example, with a Peltier device, but again even 450-540nm, let alone 400-700nm, is not likely possible.

Your best bet is probably a broad-spectrum source such as an incandescent bulb with a monchromatic optical filter.

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  • \$\begingroup\$ Temperature, you say? Well that explains that lab experiment. What about an array of LEDs; interpolating between them with temperature modulation? What kind of range can each LED cover without suffering permanent damage? \$\endgroup\$
    – sh1
    May 3, 2017 at 16:28
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LED ('Solid state device') is made up of a certain material with a specific band gap which determines the the wavelength of photon emitted. So there can be no such LED emitting all visible colors.

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The wavelength of a LED "filament" depends on the matter that it's made of and it's a static property — if you except the fact that some LEDs can change colour, e.g. green turning orange, but it requires currents much higher than rated and is a destructive operation.

Note that RGB LEDs do cover most of the visible spectrum, i.e. 390 to 700nm. Resolution is not very big however.

EDIT: This question has been asked on physics.stackexchange.com, too.

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