How to find the wavelength of incident light

How to find the wavelength of incident light

Visible light occupies the range of lengths of waves from 400 to 700 nanometers. Wavelength of the light falling on a surface and which is reflected from it can be measured by eye or by means of devices. If light polychromatic, it is necessary to consider also color of the surface.

It is required to you

  • - spectroscope with a scale;
  • - light source with the monochromator;
  • - three energy saving bulbs;
  • - computer with the LCD monitor.


1. Observe security measures. If a light source is the laser, make sure that a surface opaque. Consider that if the laser very powerful, dangerous can be also diffused light. If the source is incoherent, though monochromatic, it is much safer. But also when using they should be careful.

2. If big accuracy is not necessary, try to measure light wavelength by eye. Wavelength in 650 - 690 nanometers, orange - 590 - 600, yellow - 570 - 580, green - 510 - 520, blue - 480, blue - 450, and violet - 390 - 400 matches the red color.

3. In the presence of the spectroscope consisting of a plate with a vertical crack, prisms (or a diffraction lattice) and scales direct the device to a surface from which light is reflected, and then find wavelength on a scale.

4. In case there is no spectroscope, but there is a source reference light with the monochromator and a scale, direct this source to the same surface that the spot from it was near a spot from the checked source. Rotation of the handle achieve that spots turned out the same color, and then read indications on a scale near this handle.

5. When light is polychromatic, it is not necessary to speak about wavelength. It is only possible to define the top and lower borders of range and also to allocate the most intensive line (in a line spectrum) or peak (in continuous). For this purpose use a spectroscope with a scale. Consider that each component of a range at the same time is kind of multiplied by the same component of a range of reflection of a surface.

6. At polychromatic light close to white, determine color temperature. For this purpose look at three energy saving bulbs which color temperatures are equal 2700, 4200 and 6400 K, and measure by eye to what shade from them the shade of color of the checked source is closest. For the same purpose it is possible to use also the liquid crystal monitor: bring to it a neutral white background, and then through the menu consistently include three color temperatures stated above.

Author: «MirrorInfo» Dream Team