Lights

Commands: DISTANTLIGHT, GEOGRAPHICLOCATION,  LIGHT, LIGHTLIST, POINTLIGHT, SPOTLIGHT, SUNPROPERTIES, WEBLIGHT

Lighting is the key to make the viewer believe to look at a realistic scene.

Lighting glossary

• Ambient light: light from an unspecified source.
• Back light: light that adds depth and dimension by creating highlights.
• Distant light: light that is cast evenly throughout a scene with shadows all in the same direction.
• Fall-off: the attenuation or decrease in brightness the further from the light source.
• Fill light: the light that brightens dark areas and softens shadows from the main light.
• Point light: light that shines in all directions from a central spot.
• Spot light: focusable light that is aimed in one area.
• Photometric web: a 3D representation of the light intensity distribution of a light source.
• Web light: approximates real-world light distribution using a 3D representation of the light intensity. Web lights can be created only if the LIGHTINGUNITS system variable is set to 1 (American lighting units) or 2 (International lighting units).
• Attenuation: the fall-off in brightness the further from the light source.

General properties

The general properties are common to all lights:

• Name: a user defined name for the light.
• Type: defines the type of light: spot, point, web or distant.
• On/Off: specifies whether the light is turned on or off.
• Shadows: specifies whether the light casts shadows or not. Turning shadows off to increases performance.
• Intensity factor: multiplies the Lamp Intensity property, the result is the Resulting Intensity.
• Filter color: defines the color of the light.
• Plot glyph: if on, the light glyphs are plotted.

Spotlight hotspot and falloff properties

When a surface is illuminated by a spotlight, there is an area of maximum illumination (hotspot) that is surrounded by an area of lesser intensity (falloff).

• Hotspot angle: angle of the central light cone (defines the hotspot)
• Falloff angle: angle of the full light cone

The difference between the hotspot angle and the falloff angle defines the area of lesser light intensity.

If the falloff angle and the hotspot angle are almost equal  the edge of light cone is rather sharp (left).

The greater the difference between both angles, the softer the edge of the light cone (right).

Photometric properties

(not yet implemented)

• Lamp intensity: Defines the brightness of the light. The lamp intensity is expressed in candela (cd) which is the SI base unit of luminous intensity: the power emitted by a light source in a particular direction, weighted by the luminosity function (a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function)
• Resulting intensity: the product of the lamp intensity and and intensity factor.
• Lamp color: defines the inherent color of the light or color temperature in Kelvin or standards.

• Resulting color: this is the final color of the light: a combination of the lamp color and the filter color.
• Photometric web: If the light type is Web, Photometric Web and Web offsets are available (not implemented yet).

Geometry properties

• Position:  controls the location of the light.
• Target: defines the target point for point lights, spotlighst and weblights
• Targeted: switches the target property on/off.

Attenuation properties

In the real world, an object appears darker if it is farther away from the light source. The attenuation properties define how the light diminishes over distance.  Attenuation does not apply to photometric lights.

An alternative method to control the distance a light shines is the use of limits, which define the points from where a light starts to shine and where it stops. Using limits decreases the time needed to calculate the illumination of a scene.

Attenuation properties apply to spot lights and point lights.

• Type: the options are none, inverse linear and inverse square
• • None: no attenuation. The distance to the light source has no influence.
  • Inverse Linear: the attenuation is the inverse of the linear distance from the light: at a distance of 2 units from the light source, light is half as strong; at a distance of 4 units, light is one quarter as strong.
  • Inverse Square: the attenuation is the inverse of the square of the distance from the light: at a distance of 2 units, light is one quarter as strong; at a distance of 4 units, light is one sixteenth as strong.   
• Use Limits: if this property is set to Yes, the Start limit offset and End limit offset fields become active.
• • Start limit offset: defines the point where the light starts to shine, measured from the center of the light.
  • End limit offset: defines the point where the light stops to shine, measured from the center of the light.

To open the light list in the Drawing Explorer

Do one of the following:

• Click the Light List...  button () on the Lights toolbar.
• Choose Drawing Explorer > Lights  in the Tools menu.
• Choose Light List.. in the View | Rendering | Lights menu
• Type lightlist or LL in the command bar, then press Enter.

To define a light

1. Do one of the following:
2. Type light in the command bar, then press Enter.

The command bar reads: Enter light type [Point/Spot/Web/Distant] <Point>:

A prompt menu displays:

Choose a light type in the prompt menu.

• Click the tool button of the light type you want to create on the Lights toolbar:
• • New spot light
  • New point light
  • New distant light

2. Do one of the following:

• Specify the source position in the drawing.
• Type the coordinates of the source position in the command bar and press Enter.
• Press Enter to accept the default coordinates.

The command bar reads: Specify target position <0,0,-10>:

3. Do one of the following:

• Specify the target position in the drawing.
• Type the coordinates of the target position in the command bar and press Enter.
• Press Enter to accept the default coordinates.

The command bar reads: Enter an option to change: Name/Intensity factor/Status/Photometry/Hotspot/Falloff/shadoW/Attenuation/filterColor/<eXit>:

A prompt menu displays:

4. Do one of the following:

• Select Name  in the prompt box.
• Type N in the command bar and press Enter.

The command bar reads: Enter light name <Spotlight1>:

5. Do one of the following:

• Type a name in the command bar and press Enter.
• Press Enter to accept the default name.

The command bar reads: Enter an option to change: Name/Intensity factor/Status/Photometry/Hotspot/Falloff/shadoW/Attenuation/filterColor/<eXit>:

6. Do one of the following:

• Click a light property in the prompt menu.
• Type the capitalized letter of a light property in the command bar and press Enter.

You are prompted to define the selected property in the command bar.

7. Do one of the following to conclude the creation of the light:
8. Choose Exit in the prompt menu.
9. Press Enter.

To edit a light

1. Select the light in the drawing.
   If the Properties bar is not open yet, double click the light.

The properties of the selected light display in the Properties Bar:

2. To edit a property:
3. Expand the settings group if needed.
4. Select the property
5. Edit the selected property.
    

To define the sun properties

1. Do one of the following:
2. Click the Sun Properties... tool button () on the Render toolbar.
3. Type sunproperties or sun in the command bar, then press Enter.

The Drawing Explorer - Lights dialog displays, showing the sun properties in the Editor pane.

2. To edit a property:
3. Expand the settings group if needed.
4. Select the property
5. Edit the selected property.

To define the geographic location

1. Do one of the following:
2. Click the Geographic location... tool button () on the Render toolbar.
3. Click the Geographic location... tool button () on Editor pane of the Drawing Explorer - Lights dialog.
4. Type geographiclocation or geo in the command bar, then press Enter.

The Geographic Location dialog displays:

2. Do one of the following:
3. Type the latitude and longitude of the location in the Latitude and Longitude fields and select the appropriate hemisphere for each setting.
4. Click the Choose location... button, then select a city and timezone and click the OK button.

3. Choose a time zone in the Time Zone list.
4. Define the direction of the north.
5. Click the OK button.