Light introduction (3)

reflection refraction absorption

1. ARCHITECTURAL SERVICES RAR - 406 TOPIC – INTRODUCTION OF LIGHT SUBMITTED TO – AR. GOPAL SUBMITTED BY – TOMAR POOJA SHARMA PRATEEK SHARMA

2. LIGHT Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye. Light is a source of illumination, whether a natural one (like the sun) or an artificial one (like your lamp). Light is a form of energy that travels as waves. Their length — or wavelength — determines many of light's properties. When it comes to visible light, the highest frequency color, which is violet, also has the most energy. The lowest frequency of visible light, which is red, has the least energy.

3. CHARACTERISTICS OF LIGHT Light is an electromagnetic wave. Light travels in a straight line. Light is a transverse wave, and does not need any medium to travel. Light can travel through vaccum . Its speed through vaccum is 3 × 108 m/s. The velocity of light changes when it travels from one medium to another. The wavelength (λ) of light changes when it goes from one medium to another. The frequency (f) of the light wave remains the same in all media. Light gets reflected back from polished surfaces, such as mirrors, polished metal surfaces, etc. Light undergoes refraction (bending) when it travels from one transparent medium to another. Light does not need a material medium to travel, that is, it can travel through a vacuum too.

4. TERMINOLOGY AND UNITS LUMINANCE - Amount of light emitted from an object in a given direction. The eye can see objects because these send light to the eye. Luminance indicates how much luminous power will be detected by an eye looking at the surface from a particular angle of view. Luminance is this an indicator of how bright the surface will appear. It is measured in candelas per sq.m ( cd /m^2).

5. A LUMINAIRE- It is a complete lighting unit , consisting of a lamp or lamps together with the parts designed to distribute or enhance the light, position and protect the lamps, and connect the lamps to power supply. ILLUMINANCE - It is the ratio of the quantity of light falling on a surface and the area thatt is illuminated. Illumination is the total luminous flux incident on a surface per unit area. It is measure of how much incident light illuminates the surface.SI unit - lux or lumen /m^2

6. LUMINOUS FLUX (Lumens)- The perceived total amount of useful light from a source is the sum of the Candela measurements in all directions. It is measured in Lumens (lm). The figure is also independent of distance from the lamp and says nothing of the direction of the light, the intensity of the source or the brightness of an illuminated surface, just the total visible light in all directions.

7. WAVELENGTH- Visible light is just a small part of the spectrum of electromagnetic radiation that includes radio waves ,heat , light, microwaves etc. Each type of radiation covers a range of wavelengths that are measured in nanometers (one millionth of a millimetre ) LUMINOUS INTENSITY- Luminous intensity is a measurement the light radiating from the lamp in a particular direction disregarding the intensity of light in other directions. It measured in Candela.

8. EFFICACY- Luminous efficacy is a measures of how well a light source produces visible light . EFFICIENCY- light output from a LUMINAIRE- as a percent of light output from the bulb it uses.

9. NOMINAL POWER (Watts) Most suppliers provide a nominal power rating, rather than the actual power consumption of the lamp under specific conditions. The actual power consumption at the lamp input of most extra low voltage DC lamps at normal battery voltage is typically ten to twenty percent below the nominal.

10. PROPERTIES OF LIGHT Reflection of light Refraction of light Diffraction of light Transmission of light Propagation of light Interference of light Polarization of light Dispersion of light Scattering of light

11. REFLECTION OF LIGHT Light bounce off the surfaces like mirrors such that that angle of incidence is equal to the angle of reflection. Reflection of light enables us to see. We see colors of different objects due to reflection. We see non-luminous objects due to the reflection of light. The number of things you see in a day is due to the reflection of light .`

12. TYPES OF REFLECTION Regular reflection / Specular reflection Irregular reflection / Diffused reflection

13. REGULAR REFLECTION The nature of reflection depends on the smoothness of the surface. For example, a smooth surface of silver reflects the ray of light in one direction only. The reflection by these smooth surfaces is called regular reflection. IRREGULAR REFLECTION Most of the objects in the everyday world are not smooth on the microscopic level. The rough surfaces of these objects reflect the rays of light in many directions. Such of reflection is called irregular reflectio n.

14. LAWS OF REFLECTION OF LIGHT The laws of reflection determine the reflection of incident light rays on reflecting surfaces, like mirrors, smooth metal surfaces and clear water. Let’s consider a plane mirror as shown in the figure above. The law of reflection states that The angle of incidence is equal to the angle of reflection. The incident ray, normal ray, reflected ray at the point of an incident all lie on the same plane .`

15. REFRACTION OF LIGHT Refraction is the change in the direction of a wave passing from one medium to another One of the best examples of this is when a pencil is put in a half-filled glass of water. Notice how the pencil above the water looks normal, but under the water, it looks bent and slightly larger. This is because of refraction.

16. CAUSES OF REFRACTION A light ray refracts whenever it travels at an angle into a medium of different refractive index. This change in speed results in a change in direction. As an example, consider air travelling into water. The speed of light decreases as it continues to travel at a different angle. When light travels from air into glass, the light slows down and changes direction slightly When light travels from a less dense substance to a denser substance, the refracted light bends more towards the normal line. If the light wave approaches the boundary in a direction that is perpendicular to it, the light ray doesn’t refract in spite of the change in speed.

17. Laws of Refraction of Light

18. TYPES OF REFRACTION REFRACTION FROM RARER TO DENSER MEDIUM - in such cases, the relative refractive index is greater than 1. The angle of incidence is greater than angle of refraction. REFRACTION FROM DENSER TO RARER MEDIUM -the relative refractive index is less than 1 . The angle of refraction is less than the angle of incidence.

19. ABSORPTION OF LIGHT Light absorption is a process by which light is absorbed and converted into energy. The absorption of light is therefore directly proportional to the frequency. If they are complementary, light is absorbed. If they are not complementary, then the light passes through the object or gets reflected.

20. CAUSE OF ABSORPTION OF LIGHT At specific frequencies, the electrons of the atom tend to vibrate. When a light wave of the same natural frequency is incident on the atom, the electrons of that atom will be set into vibrational motion. During vibration, electrons interact with neighbouring atoms in such a manner it converts the vibrational energy into thermal energy. Hence, we can conclude that the selective absorption of light occurs when the frequency of the light matches the frequency at which the electrons in the atoms vibrate. Different atoms and molecules possess different natural frequencies of vibration, hence they will selectively absorb different frequencies of visible light.

21. DISPERSION OF LIGHT The process in which light is separated into it's color due to the differences in degrees of refraction. The most familiar example of dispersion is probably a rainbow, in which dispersion causes the spatial separation of a white light into components of different wavelengths (different colors).

22. INTERFERENCE OF LIGHT Interference is a phenomenon in which two waves superimpose to form a resultant wave of greater of lower amplitude. There is no loss of energy during interference. It is simply redistributed. Interference, in physics, the net effect of the combination of two or more wave trains moving on intersecting or coincident paths. Example -is the soap bubble illustrated is that reflects a variety of beautiful colors when illuminated by natural or artificial light sources.

23. POLARIZATION OF LIGHT It is defined as a phenomenon caused due to the wave nature of electromagnetic radiation. A light that is vibrating in one plane is referred to as Polarized light. And the process of transforming unpolarized light into Polarized light is known as Polarization of light Example:- Three-dimensional movies are produced and shown with the help of polarization. Polarization is used in sunglasses to reduce the glare. It is used in seismology to study earthquakes.

24. TRANSMISSION OF LIGHT A simple definition of light transmission is: When light travels through a medium such as glass without being reflected absorbed or scattered. When this happens light energy is not lost and can be considered 100% transmitted. When you shine light on an object, a number of things can happen. Reflection is when light bounces off of a surface. Specular reflection is when light reflects off of a shiny surface like a mirror. Diffuse reflection, however, is when light illuminates a dull object.

25. When light moves through a transparent (or semi-transparent) material, it can be transmitted, absorbed, or reflected. Transmission of light is when light waves move all the way through a material without being absorbed.

26. ELECTROMAGNETIC SPECTRUM Electromagnetic radiation can be expressed in terms of energy, wavelength, or frequency.Frequency is measured in cycles per second, or Hertz. Wavelength is measured in meters. Energy is measured in electron volts. Each of these three quantities for describing EM radiation are related to each other in a precise mathematical way.

27. VISIBLE SPECTRUM Visible light is a range of wavelengths in the electromagnetic spectrum visible to the human eye (wavelengths of about 390 to 700 nm).

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