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Illumination Lighting

Principle of Lighting

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Illumination Lighting

  1. 1. Vijay Balu Raskar (BE Electrical)
  2. 2. Vijay Balu Raskar (BE Electrical)
  3. 3. MAIN OBJECTS of Street Lighting Vijay Balu Raskar (BE Electrical)
  4. 4. There are no walls and ceiling which reflect or diffuse light.Hence, Direct lighting scheme can be employed.Hard Shadows and high contrast cannot be avoided.Illumination to be very large than indoor lighting.High level of illumination is not necessary.For low illumination, the eye is in its most sensitive state, so glaremust be avoided.Principle of street lighting is different from indoor lighting.High pressure sodium (HPS) lighting is being used in most of theCity. It is five times as efficient as incandescent lighting, and twice asefficient as mercury vapor lighting.HPS lights have orange-pink lamp color, and allow you to see allcolors of objects.They do not attract flying insects the way other lamps do.HPS lighting is installed to replace incandescent and mercury vaporlighting to save energy and reduce operating cost.(BE Electrical) Vijay Balu Raskar
  5. 5. “When light falls on a surface, depending upon the nature of thesurface, some portion of light energy is reflected, some portion istransmitted through medium of the surface and the rest is absorbed.” PRINICIPLE OF STREET LIGHTING:-There are two general principle:- 1) Diffusion Principle and 2) The specular reflection principle.Types of Lamps For street Lighting:-Mercury vapour and Sodium Discharge Lamps are used.They having particular advantages for street Lighting.They are lower power consumption.Discharge lamps are colour and monochromatic nature. But,no matter for street lighting. Vijay Balu Raskar (BE Electrical)
  6. 6. 1. Diffusion Principle of Street LightingExample:- Fig a Fig bWhat Is Diffused Light?ANS:-Diffused light is a soft light with neither the intensity nor the glare of direct light. It isscattered and comes from all directions. Thus, it seems to wrap around objects. It is softerand does not cast harsh shadows. Vijay Balu Raskar (BE Electrical)
  7. 7. Explanation:-Reflectors are used in this principle.They are designed to spread light uniformly and downwards.Reflectors made to have cut-off of between 30° to 45°.Filament is not visible except from underneath.The illumination at point is calculated by Inverse Square Lawmethod. Due to diffusion nature, the road surface appears bright tothe observer.Reflected light scattered in all directions.The viewed see the illuminated surface not the light Source.The diffusion nature of the road surface causes the reflectionof a certain proportion of the incident light in the direction ofobserver. Vijay Balu Raskar (BE Electrical)
  8. 8. Sometime, surface is illuminated from two lamps and resultantillumination is sum of two illuminated lamps.If surface that is uniformly illuminated by a beam of light appearsto be equally bright when viewed from all possible angle thereflection is said to be perfectly diffused. Vijay Balu Raskar (BE Electrical)
  9. 9. Fun FactThe human eye cannot see all the rays on the lightspectrum. Infrared rays, for example, are too long forthe human eye to perceive, and ultraviolet rays are tooshort. So, direct (spectral) light seems stronger thandiffuse light. However, the total light transmission is thesame. Our perception can play tricks on us. Vijay Balu Raskar (BE Electrical)
  10. 10. What Causes Light Diffusion?ANS:-When a light beam strikes a smooth surface, most of it reflects back in thesame concentration. This is specular reflection, which gives us direct, bright light. Amirror is a common example of a smooth surface that causes specular reflection. 
What happens on a rough surface?ANS:Even microscopic irregularities create roughness. The law of reflection is notbroken. Each ray reflects back at the same angle at which it struck the object but in adifferent direction. So diffuse light is scattered light. This scattering is what causes thediffusion and softness of the light beam.______________________________________________________________Application of Diffuse LightANS:-Photographers use the principle of diffuse light to create pictures with vividdetails because there are no sharp shadows to distract attention. On a sunnyday, they use light diffusers to create soft shadows. 

Horticulturists are nowdiscovering that diffused light creates a better growing environment in greenhouses.It allows for a greater horizontal spread of light and exposes the middle leaf layers tolight. 

Drivers find that wet roads have a greater glare than dry roads. That isbecause the cracks and crevices on the roads surface fill up with water, creating asmooth surface. This results in specular reflection that creates the annoying glare.Fog lamps try to make use of the principle of diffused light to provide a safer beam. Vijay Balu Raskar (BE Electrical)
  11. 11. 2. Specular Reflection Principle of Street LightingExample:- Fig a Fig bThis method is more economical than diffusion method.This method produces “Glare for the motorists” Vijay Balu Raskar (BE Electrical)
  12. 12. Vijay Balu Raskar (BE Electrical)
  13. 13. Explanation:-Reflectors are used in this principle but curved upwards.They are designed to spread light very large angle of incidentReflectors made to thrown light to large angle.Filament is visible.The illumination at point is calculated by Lambert’s CosineLaw method. Due to Reflection nature, the road surface or object shown30 meter away to the observer.A beam of light reflected but not scattered.This method is suitable for straight sections of the road.The viewed see the illuminated surface and the light Source. This method produces “Glare for the motorists”The illumination required depends upon the class of steetlighting installation. Vijay Balu Raskar (BE Electrical)
  14. 14. Vijay Balu Raskar (BE Electrical)
  15. 15. Vijay Balu Raskar (BE Electrical)
  16. 16. COMPARISION Vijay Balu Raskar (BE Electrical)