Siddharth Pandit

Ok, here I am going to explain some basic terms about 3D lighting. Light is defined in physics as packets of energy units called photons. In real life the, the sub light or white light that we see is a harmony of different wave lengths each interpreted colors in a spectrum as shown below.

The above is what we call as the visible spectrum of light that our eyes and our brain can coherently interpret. The range referred to as infrared and ultraviolet are not visible to the human eye. White light is a combination of all visible wavelengths and the reason why we see apple red and grapes green because these objects only reflect the wavelength corresponding to their color definition. So, a green leaf would absorb every wavelength except green which it reflects and is understood by our brain as green. This is why color is so important to us and throughout cinematic history, a delicate balance of light, colors and shadows has ensured that the audience no t only enjoys the movie plus also goes one step beyond reality in to a dimension that we define as fantasy and the make believe.

Followings are some important term associated with lighting

Direct and Indirect Illumination – in real life, wherever light strikes, the area is referred to directly illuminated whereas areas in the shadow are dimply lit as a result of lighting bouncing off from various objects and are referred to as in direct illuminated. This forms basis Global Illumination in CG.

Radiosity – When light bounces off brightly colored objects it carries colors of the object as well and causes a halo or shad e on neutral colored objects like a bright red object on a white base causes a reddish hue near the object. This phenomenon is called color bleeding or Radiosity. A subset feature of global Illumination, raidosity is one of those details which are important for photorealism.

Shadows – Defining shadows is much more that calling it the dark area created on the other side of the lit surface. Shadows can tell us a lot about the size of light, the distance of object from the light and the refract ability of the shadow casting medium. The theatre and the cinema have been able to use shadow as medium for conveying portions of the story which are too obvious or unfit to be shown directly.

Having understood above, lighting in computer graphics presents its own challenges. For instance, consider the following facts

• Light in CG do not indirectly illuminate unless we use special programs called GI renders.
• There are typically more than two types of shadow options in any 3D software.
• Radiosity dose not happen automatically and has to be optionally simulated at the cost of render time, just like GI.
• Lights in CG do not attenuate automatically and travel to infinity unless specified.

As you can see, lighting in CG means more than merely switching a bulb on or off.