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Light sources can be assigned the shadowless keyword and no
shadows will be cast due to its presence in a scene. Sometimes, scenes are
difficult to illuminate properly using the lights we have chosen to
illuminate our objects. It is impractical and unrealistic to apply a higher
ambient value to the texture of every object in the scene. So instead, we
would place a couple of fill lights around the scene. Fill lights
are simply dimmer lights with the shadowless keyword that act to
boost the illumination of other areas of the scene that may not be lit well.
Let's try using one in our scene.
Remember the three colored area spotlights? We go back and un-comment them and comment out any other lights we have made. Now we add the following:
light_source {
<0, 20, 0>
color Gray50
shadowless
}
This is a fairly dim light 20 units over the center of the scene. It will give a dim illumination to all objects including the plane in the background. We render it and see.
Light sources are invisible. They are just a location where the light
appears to be coming from. They have no true size or shape. If we want our
light source to be a visible shape, we can use the looks_like
keyword. We can specify that our light source can look like any object we
choose. When we use looks_like, then no_shadow is
applied to the object automatically. This is done so that the object will not
block any illumination from the light source. If we want some blocking to
occur (as in a lampshade), it is better to simply use a union to do the same
thing. Let's add such an object to our scene. Here is a light bulb we
have made just for this purpose:
#declare Lightbulb = union {
merge {
sphere { <0,0,0>,1 }
cylinder {
<0,0,1>, <0,0,0>, 1
scale <0.35, 0.35, 1.0>
translate 0.5*z
}
texture {
pigment {color rgb <1, 1, 1>}
finish {ambient .8 diffuse .6}
}
}
cylinder {
<0,0,1>, <0,0,0>, 1
scale <0.4, 0.4, 0.5>
texture { Brass_Texture }
translate 1.5*z
}
rotate -90*x
scale .5
}
Now we add the light source:
light_source {
<0, 2, 0>
color White
looks_like { Lightbulb }
}
Rendering this we see that a fairly believable light bulb now illuminates the scene. However, if we do not specify a high ambient value, the light bulb is not lit by the light source. On the plus side, all of the shadows fall away from the light bulb, just as they would in a real situation. The shadows are sharp, so let's make our bulb an area light:
light_source {
<0, 2, 0>
color White
area_light <1, 0, 0>, <0, 1, 0>, 2, 2
adaptive 1
jitter
looks_like { Lightbulb }
}
We note that we have placed this area light in the x-y-plane instead of the x-z-plane. We also note that the actual appearance of the light bulb is not affected in any way by the light source. The bulb must be illuminated by some other light source or by, as in this case, a high ambient value.
If it is realism we want, it is not realistic for the plane to be evenly
illuminated off into the distance. In real life, light gets scattered as it
travels so it diminishes its ability to illuminate objects the farther it
gets from its source. To simulate this, POV-Ray allows us to use two
keywords: fade_distance, which specifies the distance at which
full illumination is achieved, and fade_power, an exponential
value which determines the actual rate of attenuation. Let's apply these
keywords to our fill light.
First, we make the fill light a little brighter by changing
Gray50 to Gray75. Now we change that fill light as
follows:
light_source {
<0, 20, 0>
color Gray75
fade_distance 5
fade_power 1
shadowless
}
This means that the full value of the fill light will be achieved at a distance of 5 units away from the light source. The fade power of 1 means that the falloff will be linear (the light falls off at a constant rate). We render this to see the result.
That definitely worked! Now let's try a fade power of 2 and a fade distance of 10. Again, this works well. The falloff is much faster with a fade power of 2 so we had to raise the fade distance to 10.
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