Reference:Light Source - Revision history

Clipka: canonicalize some version numbers

2021-06-09T14:42:39Z

canonicalize some version numbers

Clipka: /* Light Fading */ canonicalize a version number

2021-06-09T14:39:57Z

Light Fading: canonicalize a version number

Jholsenback: grammar

2021-04-29T21:50:29Z

grammar

Maurice: Inserted a Clipka quote about area lights fading

2021-04-25T16:31:32Z

Inserted a Clipka quote about area lights fading

Jholsenback: corrections

2021-01-31T19:03:31Z

corrections

Jholsenback: suggested addition and general cleanup

2021-01-31T18:47:14Z

suggested addition and general cleanup

Jholsenback: version update

2017-06-30T08:45:18Z

version update

Jholsenback: version changes

2017-06-26T10:37:57Z

version changes

Jholsenback: author corrections

2016-12-26T10:36:25Z

author corrections

Jholsenback: minor changes

2016-12-23T10:50:22Z

minor changes

@@ Line 612: / Line 612: @@
 scene. This behavior can be switched off by using <code>media_interaction off</code>
 inside the light source statement. </p>
-<p class="Note"><strong>Note:</strong> In POV-Ray 3.0 this feature was turned off
+<p class="Note"><strong>Note:</strong> In POV-Ray v3.0 this feature was turned off
 and on with the <code>atmosphere</code> keyword.</p>
@@ Line 624: / Line 624: @@
 distance-based, exponential intensity falloff ruled by the used fog or media.
 If there is no fog or media no change will be seen.</p>
-<p class="Note"><strong>Note:</strong> In POV-Ray 3.0 this
+<p class="Note"><strong>Note:</strong> In POV-Ray v3.0 this
 feature was turned off and on with the <code>atmospheric_attenuation</code> keyword.</p>

@@ Line 603: / Line 603: @@
 <p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc. If this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes. When dealing with area light sources the <code>fade_distance</code> should be, as a rule of thumb, about the same order of magnitude as the area light's dimensions.</p>
-<p>{{New}} in POV-Ray 3.8 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode <em>requires</em> <code>#version 3.8</code> or higher to be set.</p>
+<p>{{New}} in POV-Ray v3.8 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode <em>requires</em> <code>#version 3.8</code> or higher to be set.</p>
 ==Atmospheric Media Interaction==

@@ Line 601: / Line 601: @@
 <p>At first glance this may seem counter-intuitive but it works out well given the small value used for <em>Fade_Distance</em>. You should be aware that this method is meant to give a light strength value of <em>ONE</em> at the point of interest <em>ONLY</em>. In other words, the point represented by the calculated value <em>Light_Distance</em> in the above example. Naturally objects closer to the light source will get a stronger illumination, while objects further away will receive less.</p>
-<p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc. It follows that as a rule of thumb, fade_distance of an area light source should also be about the same order of magnitude as the area light's dimensions; if this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes.</p>
+<p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc. If this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes. When dealing with area light sources the <code>fade_distance</code> should be, as a rule of thumb, about the same order of magnitude as the area light's dimensions.</p>
 <p>{{New}} in POV-Ray 3.8 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode <em>requires</em> <code>#version 3.8</code> or higher to be set.</p>

@@ Line 601: / Line 601: @@
 <p>At first glance this may seem counter-intuitive but it works out well given the small value used for <em>Fade_Distance</em>. You should be aware that this method is meant to give a light strength value of <em>ONE</em> at the point of interest <em>ONLY</em>. In other words, the point represented by the calculated value <em>Light_Distance</em> in the above example. Naturally objects closer to the light source will get a stronger illumination, while objects further away will receive less.</p>
-<p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc.; if this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes.</p>
+<p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc. It follows that as a rule of thumb, fade_distance of an area light source should also be about the same order of magnitude as the area light's dimensions; if this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes.</p>
 <p>{{New}} in POV-Ray 3.8 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode <em>requires</em> <code>#version 3.8</code> or higher to be set.</p>

@@ Line 299: / Line 299: @@
 <p>Parallel lights are useful for simulating very distant light sources, such as sunlight. As the name suggests, it makes the light rays parallel. This is done by shooting rays from the closest point on a plane to an object intersection point. That plane is a perpendicular which is defined by the light <code>location</code> and the <code>point_at</code> vectors.</p>
-<p>Two things must be considered when choosing the light location
+<p>These things must be considered when choosing the light location
-(specifically, its distance):</p><ol>
+(specifically, its distance):</p><ul>
 <li>Any part of an object <em>above</em> the light plane still gets illuminated according to
 the light direction, but they will not cast or receive shadows.</li>
 <li><code>fade_distance</code> and <code>fade_power</code> use the lights
 <code>location</code> to determine distance for attenuation, so that the attenuation will still look like that of a point source.</li>
-<li>The <code>area_light</code> also uses the lights <code>location</code> in its calculations.</li></ol>
+<li>The <code>area_light</code> also uses the lights <code>location</code> in its calculations.</li></ul>
 <p class="Note"><strong>Note:</strong> For non fading lights, you only need to make <code>location</code> just distant enough from the center that it is farther than the farthest other objects in your scene.</p>

@@ Line 284: / Line 284: @@
 {{#indexentry:point_at, light_source}}
 {{#indexentry:keyword, point_at}}
 <pre>
 light_source {
    LOCATION_VECTOR, COLOR
@@ Line 295: / Line 294: @@
 </pre>
 <p class="Note"><strong>Note:</strong> For normal point lights, <code>point_at</code> must come after
 <code>parallel</code>.</p>
-<p>Parallel lights are useful for simulating very distant light sources, such as
+<p>Parallel lights are useful for simulating very distant light sources, such as sunlight. As the name suggests, it makes the light rays parallel. This is done by shooting rays from the closest point on a plane to an object intersection point. That plane is a perpendicular which is defined by the light <code>location</code> and the <code>point_at</code> vectors.</p>
 <p>Two things must be considered when choosing the light location
 (specifically, its distance):</p><ol>
-<li>Any parts of an object <em>above</em> the light plane still get illuminated according to
+<li>Any part of an object <em>above</em> the light plane still gets illuminated according to
 the light direction, but they will not cast or receive shadows.</li>
-<li><code>fade_distance</code> and <code>fade_power</code> use the light
+<li><code>fade_distance</code> and <code>fade_power</code> use the lights
-<code>location</code> to determine distance for light attenuation, so the attenuation
+<code>location</code> to determine distance for attenuation, so that the attenuation will still look like that of a point source.</li>
-still looks like that of a point source.
+<li>The <code>area_light</code> also uses the lights <code>location</code> in its calculations.</li></ol>
-<br>Area light also uses the light location in its calculations.</li></ol>
+<p class="Note"><strong>Note:</strong> For non fading lights, you only need to make <code>location</code> just distant enough from the center that it is farther than the farthest other objects in your scene.</p>
 ==Area Lights==

@@ Line 609: / Line 609: @@
 <p class="Note"><strong>Note:</strong> For maximum realism, use <code>fade_power 2</code> and set <code>fade_distance</code> to the approximate radius of the object supposedly giving off the light, e.g. the radius of a frosted incandescent light bulb, half the length of the tungsten filament in a clear incandescent light bulb, etc.; if this makes the light seem too dim, compensate by boosting the light source brightness. There is nothing wrong with a light source having a color of <code>rgb &lt;10000,8000,2000&gt;</code> if that's what it takes.</p>
-<p>{{New}} in POV-Ray 3.7.1 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode requires <code>#version</code> to be set to <code>3.71</code> or higher.</p>
+<p>{{New}} in POV-Ray 3.8 is an alternative mode for distance-based light fading, in which the light intensity follows an inverse power law at all distances. To activate this mode, specify <code>fade_distance 0</code>. Nominal light intensity is then achieved at unit distance. For backward compatibility, this mode requires <code>#version</code> to be set to <code>3.71</code> or higher.</p>
 ==Atmospheric Media Interaction==

@@ Line 568: / Line 568: @@
 <p>A value for the light source intensity can be easily calculated when you take into account the distance from the light source to the scene center, or the object to be illuminated, and you set a relatively small value for <code>fade_distance</code> e.g.: the size of the light itself, relative to the scene dimensions.</p>
-<p>The following example, that takes the inverse of the above formula that was used to calculate the factor by which the light is attenuated.</p>
+<p>The following example, that takes the reciprocal of the above formula that was used to calculate the factor by which the light is attenuated.</p>
 <pre>
 // setup the function
-#declare Intensity_Factor = function (LD,FD,FP) {pow(1+(LD/FD),FP)/2};
+#declare Intensity_Factor = function (LD,FD,FP) {(1+pow(LD/FD,FP))/2};
 // the translated position of the light source