UNDERSTANDING LIGHTS FOR ITS APPLICATION IN 3D GRAPHICS

The goals of lighting in 3D computer graphics are more or less the same as those of real world lighting. Lighting serves a basic function of bringing out, or pushing back the shapes of objects visible from the camera's view. It gives a two-dimensional image on the monitor an illusion of the third dimension-depth. But it does not just stop there. It gives an image its personality, its character. A scene lit in different ways can give a feeling of happiness, of sorrow, of fear etc., and it can do so in dramatic or subtle ways. Along with personality and character, lighting fills a scene with emotion that is directly transmitted to the viewer

Before giving lights actually to a scene one must ask question to itself…
Is it an interior or exterior scene?Is the time of day/night important to your scene?Is there a particular mood or atmosphere you are trying to portray?What objects do you want to draw the audience's attention to and in what order?What type of shadowing do you want to use in your scene and how are you going to accomplish it?

In any type of the scene. unless the scene is indoor and no outdoor light is coming.
The day light which has sun light and sky light is need to understand thoroughly…Photographers and painters necessarily have a better understanding of light, but light is a crucial element of any art. Without understanding it well it is very hard to achieve realism.



THE FUNDAMENTALS

Here it illustrates a sunny afternoon. The main source of light is the sun, whilst the blue sky supplies a second source of light with very different characteristics. Some light is also bouncing between the white base and the ball and supplies a third source of light

The brightest light is coming from the sun and is white light emanating from a small source, which causes it to cast sharp edged shadows. The second source, the blue sky, is a very large light source and as a result has very soft shadows (which in any case are completely masked by the direct light coming from the sun). I will go into more detail later about light sources and shadow size, but for now just remember that the smaller the source of the light, the harder the shadows.
The light coming from the blue sky has a very strong colour cast which affects everything in this scene. The shadow cast by the ball is blue because it is illuminated by blue skylight, since the ball is shielding it from the white light of the sun. The parts of the ball which aren't in direct sunlight also take on a blue hue because they are lit by the blue sky.
Finally the light that is reflected between the card and the ball is also predominantly blue (even though the card and ball are white) since it is blue skylight that is being reflected by the white objects. The surfaces which are closer together receive more of this reflected light than areas which are further apart, therefore the bottom part of the ball is lighter than the centre because it is nearer the white card.
The darkest areas in the image are the base of the cast shadow and the border between the areas in sunlight and shade on the ball: this zone is called the terminator. The base of the cast shadow is very dark because it receives no sunlight and the ball is also masking it from most of the skylight and bounced light. The other end of the cast shadow is lighter because it is receiving more light from the sky and also bounced light from the ball.





Why is the light from the sky is blue?

Visible light is made up of tiny particles called photons, these particles have different wavelengths depending on their colour: blue light comprises of particles with shorter wavelengths whereas red light is made of particles with longer wavelengths.

White light from the sun is made up of a continuous spectrum of colours which, conventionally, is divided into the colours of the rainbow (with progressively longer wavelengths: violet, indigo, blue, green, yellow, orange and red). It is the mixture of these colours that produces white.However what happens to light when it travels through the atmosphere of the earth is that the shorter wavelengths of light become scattered. Our atmosphere is made from various gases and the atoms and molecules that these are formed from are suspended within it. Photons travelling through the atmosphere physically collide with these atomic particles and a collision will deflect the photons and make them bounce in another direction. Shorter wavelengths are more likely to be deflected than longer ones, so that the photons which are scattered in all directions by these collisions are predominantly blue.




Longer wavelengths of light, such as red, can travel further through the atmosphere without being scattered. This is why sunsets are red: as the sunlight travels through a thicker layer of air to reach us when it is lower in the sky a lot of the blue light is lost from scattering, and the remaining light is predominantly red.


Light bounces

When light hits a surface it either bounces or is absorbed by it, depending on what colour that surface is. A white object will reflect all wavelengths equally, whereas a black object will absorb them all. When white light hits a red surface the blue and green wavelengths are absorbed and the red light is reflected (I'm just using the primary colours, rather than the full spectrum here, for the sake of simplicity).
So if white light hits a red surface the photons this surface reflects will be red. When these photons hit the next surface in their path they will therefore be illuminating it with red light. This phenomenon is called radiance, and the colours of adjacent objects will have an affect on each other because of this