Principles of Light

1. Principles of Light A Lecture By: AMIT CHAWLA

2. Fundamental of Photography • LIGHT – Raw Material of SIGHT • Features of Light • Light travels in Straight Line (within common substance of uniform composition) until obstructed. • Light travels at a great speed (3,00,000 Km/Sec through vacuum). Inversely dependent on medium’s density. • Light moves like waves; like ripples in water. Different wavelengths give sensation of colours • Light contains energy particles called Photons.

3. AIR GLASS Light travels in Straight Line • This applies only within common substance of uniform composition. But what happens when it reaches a surface. Three Cases: • Reflection • Refraction • Absorption

4. Reflection When the reflecting surface is smooth and polished, the reflection is orderly, or specular. Specular light is reflected at the same angle to the surface as the light incident to the surface When the object surface is not smooth and polished but irregular, light is reflected irregularly or diffused; i.e. the light is reflected in more than one direction. Practically all surfaces reflect both specular and diffused  light

5. Refraction | Absorption REFRACTION The change of direction that occurs when a ray of light passes from one transparent substance into another substance of different density is called refraction. ABSORPTION When light strikes a medium and is neither reflected nor transmitted (passed on), it is said to be absorbed.

6. Refraction • Other Cases: • DIFFRACTION • DISPERSION

7. Light travels at a great speed • Light travels at a great speed (3,00,000 Km/Sec or 186,000 Miles/sec through vacuum). It is inversely dependent on medium’s density. Therefore the speed of Light is marginally slower in Air and still slightly slower in denser substances like water and glass

8. Light moves like waves • What you recognise as light is just a part of an enormous range of ‘Electromagnetic Radiations’.

9. Basic wavelengths &The Human Eye • The human eye seems to contain three kind of light receptors responding to broad-overlapping bands of Blue, Red and Green. • In the later parts of our discussion you will find how concept of 3 human receptors together responding to the full colour system is adapted to make colour photographic films too.

10. But how do we see things? The rays of light, controlled by the IRIS, enter our eyes and hit the LENS present in the eye. The lens converges the light which falls on the retina. These rays then excite the nerves (Cones and Rods), which carry message to the brain through optic nerve.

11. How is Photo / Light Captured on Camera? Working Of Camera ≈ Human Vision Concept • Both have: • Lens • Iris • Recording Medium

12. Other Hidden Things Focus Just like a camera, our eyes also need to focus. Ever tried this exercise? inside our eyes This process is performed by the lens tissues. In cameras this is done by Optical Lenses.

13. Other Hidden Things Time of Exposure Most of us have this belief that our eyes see continuous motion. NO! This is Untrue. Eyes capture only a frame at a time just like a photograph. But when we see successive frames, we perceive motion. Cameras capture light by fast action of opening and closing of a shutter.

14. Wrapping up • Principles & Features of Light • How do we see things? • Camera v/s Human Eye. • ANY DOUBTS??? NEXT CLASS – HOW PHOTOGRAPHY WORKS