|
 |
Nieminen Mika wrote in message <6h5a76$3em$2@oz.aussie.org>...
>POVRAY (POV### [at] aol com) wrote:
> I wonder why the illumination of an object depends on the incident
>angle of the light in real world. I just can't figure it. Has this
>something to do with the amount of light per area unit of the surface?
Well, looks like you already got it there!
This is the same reason, as for why the vineyards in the "relatively"
northern parts of Germany have to be sloped (to catch enough son), while the
ones in Italy (or California) don't have to care about that. Sun-collectors
on rooftops are also a good example: they are always perpendicualr to the
main sun direction.
Imagine that you could "count" the rays of the sun. Now imagine the sun
standing perpendicular to the earth's surface (like it can only happen
around the equator). You could then mark off a, lets say, 1 square meter
area and somehow "mark" the sunbeams that define the corners of that square.
Now angle the surface (in respect to the rays) and look at the shape that is
now defined by those four rays: It is now longer a square, but a
prespectively warped rectangle. And the area of this "shape" is larger than
the area of the original square and it will get even larger when you
increase the angle.
But the "number" of rays falling on this increasing area is still the same!
So (very simply put): The same amount of light falls on a larger area, thus,
while the area in total gets the same light, each square centimeter gets
less light (or less sun-energy, when going back to the vineyard /
sun-collector analogy).
Johannes.
Post a reply to this message
|
|
