When is reflection of light said to occur

Since the angle of incidence and the angle of reflection are the same or equal, a beam of parallel rays falling on a smooth surface is reflected as a beam of parallel light rays in one direction only. It is explained below in the figure. In diffuse reflection, a parallel beam of incident light is reflected in different directions. In this case, the parallel incident rays do not remain parallel after reflection, they are scattered in different directions. It is also known as irregular reflection or scattering and so, takes place from rough surfaces like that of paper, cardboard, chalk, table, chair, walls and unpolished metal objects.

Since, the angle of incidence and angle of reflection are different, the parallel rays of light falling on a rough surface go in different directions as explained below in the figure. Before understanding the laws of reflection of light, lets understand the meaning of some important terms such as, incident ray, reflected ray, point of incidence, normal at the point of incidence , angle of incidence and angle of reflection.

Incident ray: The ray of light falling on the surface of a mirror is called incident ray. Point of incidence: The point at which the incident ray falls on the mirror surface is called point of incidence.

Reflected ray: The ray of light which is sent back by the mirror from the point of incidence is called reflected ray. Normal: A line perpendicular or at the right angle to the mirror surface at the point of incidence is called normal. Angle of incidence: The angle made by the incident ray with the normal is called angle of incidence. Angle of reflection: The angle made by the reflected ray with the normal at point of incidence is called angle of reflection.

Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light. Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects. When light waves of these frequencies strike an object, the electrons in the atoms of the object begin vibrating.

But instead of vibrating in resonance at a large amplitude, the electrons vibrate for brief periods of time with small amplitudes of vibration; then the energy is reemitted as a light wave. If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object.

Such frequencies of light waves are said to be transmitted. If the object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material.

Rather the electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of light are said to be reflected. The color of the objects that we see is largely due to the way those objects interact with light and ultimately reflect or transmit it to our eyes.

The color of an object is not actually within the object itself. Rather, the color is in the light that shines upon it and is ultimately reflected or transmitted to our eyes. We know that the visible light spectrum consists of a range of frequencies, each of which corresponds to a specific color.

When visible light strikes an object and a specific frequency becomes absorbed, that frequency of light will never make it to our eyes. Any visible light that strikes the object and becomes reflected or transmitted to our eyes will contribute to the color appearance of that object.

So the color is not in the object itself, but in the light that strikes the object and ultimately reaches our eye. The only role that the object plays is that it might contain atoms capable of selectively absorbing one or more frequencies of the visible light that shine upon it. So if an object absorbs all of the frequencies of visible light except for the frequency associated with green light, then the object will appear green in the presence of ROYGBIV.

And if an object absorbs all of the frequencies of visible light except for the frequency associated with blue light, then the object will appear blue in the presence of ROYGBIV. Consider the two diagrams below. The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light.

Such chemicals that are capable of selectively absorbing one or more frequency of white light are known as pigments. We can see that the rays will bend as the wave passes from air to glass. The bending occurs because the wave fronts do not travel as far in one cycle in the glass as they do in air.

As the diagram shows, the wave front halfway into the glass travels a smaller distance in glass than it does in air, causing it to bend in the middle. Thus, the ray, which is perpendicular to the wave front, also bends. The situation is like a marching band marching onto a muddy field at an angle to the edge of the field. The rows bend as the speed of the marchers is reduced by the mud.

The amount of bending depends on the angle of incidence and on the indices of refraction of glass and air, which determine the change in speed.

Reflection Reflection is the abrupt change in the direction of propagation of a wave that strikes the boundary between two different media.

Specular reflection occurs at smooth, plane boundaries. This is Snell's law , or the law of refraction. This method of "piping" light can be maintained for long distances and with numerous turns along the path of the fiber. Total internal reflection is only possible under certain conditions.

The light is required to travel in a medium that has relatively high refractive index, and this value must be higher than that of the surrounding medium. Water, glass, and many plastics are therefore suitable for use when they are surrounded by air. If the materials are chosen appropriately, reflections of the light inside the fiber or light pipe will occur at a shallow angle to the inner surface see Figure 7 , and all light will be totally contained within the pipe until it exits at the far end.

At the entrance to the optic fiber, however, the light must strike the end at a high incidence angle in order to travel across the boundary and into the fiber. The principles of reflection are exploited to great benefit in many optical instruments and devices, and this often includes the application of various mechanisms to reduce reflections from surfaces that take part in image formation.

The concept behind antireflection technology is to control the light used in an optical device in such a manner that the light rays reflect from surfaces where it is intended and beneficial, and do not reflect away from surfaces where this would have a deleterious effect on the image being observed.

One of the most significant advances made in modern lens design, whether for microscopes, cameras, or other optical devices, is the improvement in antireflection coating technology. Examine how various combinations of antireflection coatings affect the percentage of light transmitted through, or reflected from, a lens surface.

The tutorial also investigates reflectivity as a function of incident angle. Thin coatings of certain materials, when applied to lens surfaces, can help reduce unwanted reflections from the surfaces that can occur when light passes through a lens system.

Modern lenses that are highly corrected for optical aberrations generally have multiple individual lenses, or lens elements, which are mechanically held together in a barrel or lens tube, and are more properly referred to as a lens or optical system. Each air-glass interface in such a system, if not coated to reduce reflections, can reflect between four and five percent of an incident light beam normal to the surface, resulting in a transmission value of 95 to 96 percent at normal incidence.

Application of a quarter-wavelength thick antireflection coating having a specifically chosen refractive index can increase the transmission value by three to four percent.

Modern objective lenses for microscopes, as well as those designed for cameras and other optical devices, have become increasingly more sophisticated and complex, and may have 15 or more separate lens elements with multiple air-glass interfaces. If none of the elements were coated, reflection losses in the lens from axial rays alone would reduce transmittance values to around 50 percent. In the past, single-layer coatings were used to reduce glare and improve light transmission, but these have been largely supplanted by multilayer coatings that can produce transmittance values exceeding The incident wave strikes the first layer Layer A in Figure 8 at an angle, resulting in part of the light being reflected R 0 and part being transmitted through the first layer.

Upon encountering the second antireflection layer Layer B , another portion of the light R 1 is reflected at the same angle and interferes with light reflected from the first layer.

Some of the remaining light waves continue on to the glass surface where they are again partially reflected and partially transmitted. Light that is reflected from the glass surface R 2 interferes both constructively and destructively with light reflected from the antireflection layers. The refractive indices of the antireflection layers differ from that of the glass and the surrounding medium air , and are carefully chosen according to the composition of the glass used in the particular lens element to produce the desired refraction angles.

As the light waves pass through the antireflection coatings and the glass lens surface, nearly all of the light depending upon the angle of incidence is ultimately transmitted through the lens element and focused to form an image. Magnesium fluoride is one of many materials used for thin-layer optical antireflection coatings, although most microscope and lens manufacturers now produce their own proprietary coating formulations.

The general result of these antireflection measures is a dramatic improvement of image quality in optical devices because of increased transmission of visible wavelengths, reduction of glare from unwanted reflections, and elimination of interference from unwanted wavelengths that lie outside the visible light spectral range.

The reflection of visible light is a property of the behavior of light that is fundamental in the function of all modern microscopes. Light is often reflected by one or more plane or flat mirrors within the microscope to direct the light path through lenses that form the virtual images we see in the oculars eyepieces.

Microscopes also make use of beamsplitters to allow some light to be reflected while simultaneously transmitting a portion of the light to different parts of the optical system. Other optical components in the microscope, such as specially designed prisms, filters, and lens coatings, also carry out their functions in forming the image with a crucial reliance on the phenomenon of light reflection.

Thomas J. Fellers and Michael W. Introduction to the Reflection of Light. Reflection of Light When light waves are incident on a smooth, flat surface, they reflect away from the surface at the same angle as they arrive.