Subject: Re: ambient lighting...
From: Ernie Wright <[email-masked]>
To: Multiple recipients of list <[email-masked]>
Date: Thu, 18 Jan 1996 05:15:44 -0500

Adrian Onsen wrote:

> 	When you set the "reflectivity" of an object, does that affect 
> the amount of LIGHT reflected off the object or just the image being 
> reflected.

Reflectivity is specifically for mirror-like effects.  It's used to
set how much of the environment is visible on the surface.  It can't
be used to bounce light.

> 	The reason I'm asking, is because in reality, I can have only
> one light source in a room, and have the ENTIRE room lit up!

In the real world, light keeps bouncing around.  The brightness of a
wall is determined by the amount of light it receives from the lamp,
plus the light reflected off of everything else in the room.  In LW,
the brightness depends solely on the light source.  Real world light
bouncing is simulated with the Ambient setting.

The shortcoming of the ambient simulation is that everything in the
scene gets the same amount of bounced light, while in the real world
objects close to a dark floor will receive a lot less indirect light
than things facing a white ceiling.

Radiosity is a much more accurate solution of the so-called diffuse 
interaction problem.  Surfaces are broken up into patches of constant
brightness, and then each patch is checked for interaction with all of
the others.  It's not unusual for radiosity-rendered images to take
days or weeks to render.  But as textbooks are fond of pointing out,
radiosity calculations are view-independent, so if the only thing that
moves is the camera, the calculations only have to be done *once*.
You can then fly the camera around in real time, which is why one of
the suggested practical applications is architectural walk-throughs.

- Ernie