The reed switch is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. They are often used in alarm systems, on bicycles for wheel speed measurement and in many other devices. Here we will say few words about reed switch and show you very interesting video how they are made

Light.Visible light is an electromagnetic wave in range of 400 to 700nm. This is just a small part of all existing wavelengths. The light that we see is not one wavelength but a combination of many wavelengths.
The spectral power distribution - SPD shows the precise dependence of the color in function of light source in the form of diagram that represents energy at each wavelength in the visible spectrum.