![]() ![]() Reflectance ρ, Transmittance τ and Absorptance α The measurement of classical transmission and reflection with a handheld device requires measuring systems with intelligent correction methods.įig. 1: top: Direct, mixed and diffuse reflection bottom: direct, mixed and diffuse transmissionįig. 2: When directly reflected or directly transmitted, a unidirectional beam follows the laws of geometrical optics:ĭirect reflection (left): αi n = α out, direct transmission (right): n 1 × sin( α in) = n 2 × sin( α out) with n 1 and n 2 denoting the respective medium’s index of refraction.For the measurement of scattering samples we would like to refer to a spectrophotometer specially designed for this purpose.For the optical measurement of reflection, transmission, absorption, and photoluminescence integrating sphere measuring systems are suitable. ![]() Exception: The Doppler Effect causes a change in frequency when the reflecting material or surface is in motion.Ībsorption is the transformation of radiant power to another type of energy, usually heat, by interaction with matter. Reflection, transmission and scattering leave the frequency of the radiation unchanged. In this case, we speak about regular reflection (or s pecular reflection) and regular transmission (or direct transmission). When no diffusion occurs, reflection or transmission of a unidirectional beam results in a unidirectional beam according to the laws of geometrical optics (Fig. 2). In this case, we speak about diffuse reflection and diffuse transmission (Fig. 1). Both processes can be accompanied by diffusion (also called scattering), which is the process of deflecting a unidirectional beam into many directions. If all of these colours of light are shone onto a screen at the same time, you will see white.Reflection is the process by which electromagnetic radiation is returned either at the boundary between two media (surface reflection) or at the interior of a medium (volume reflection), whereas transmission is the passage of electromagnetic radiation through a medium. Red, green and blue are the primary colours for additive mixing. When coloured lights are mixed together, it is called additive mixing. For example, red and green lights are used to make our brain perceive the image as yellow. If you look at a screen with a magnifying glass you will be able to see that only these three colours are being used. This is how TV and computer screens work. Mixing these colours in different proportions can make all the colours of the light we see. The primary colours of light are red, green and blue. Some estimate that humans are able to distinguish about 10 million colours. These three types of colour receptor allow the brain to perceive signals from the retina as different colours. (These cones have traditionally been known as blue-sensitive, green-sensitive and red-sensitive, but as each cone is actually responsive to a range of wavelengths, the S, M and L labels are more accepted now.) There are three types of cones in the human eye that are sensitive to short (S), medium (M) and long (L) wavelengths of light in the visible spectrum. Black objects absorb all colours so no light is reflected. White objects appear white because they reflect all colours. If only blue light is shone onto a red shirt, the shirt would appear black, because the blue would be absorbed and there would be no red light to be reflected. Red light is the only light that is reflected from the shirt. The colours we see are the wavelengths that are reflected or transmitted.įor example, a red shirt looks red because the dye molecules in the fabric have absorbed the wavelengths of light from the violet/blue end of the spectrum. Objects appear different colours because they absorb some colours (wavelengths) and reflected or transmit other colours. Extreme care must be taken to ensure that light from a laser never enters someone’s eyes.) Colour of objects (Lasers are extremely dangerous and can cause permanent eye damage. Light from a laser is monochromatic, which means it only produces one colour. Light from a torch or the Sun is a good example of this. White light is actually made of all of the colours of the rainbow because it contains all wavelengths, and it is described as polychromatic light.
0 Comments
Leave a Reply. |