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

Lighting glossary

  • Ambient light: light from an unspecified source.
  • Distant light: light from an infinitely far source. This causes the complete scene to be lit from the same direction.
  • Fall-off: the attenuation or decrease in brightness the further from the light source.
  • Point light: light that shines in all directions from a central point.
  • Spot light: focusable light that is aimed to one area.
  • 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.

System variables

LIGHTINGUNITS (Lighting units):

  • 0: Generic lighting - this obsolete option can no longer be set but may exist in older drawings.
  • 1: Enables Photometric lighting using American units: Foot-Candles.
  • 2: Enables Photometric lighting using International units: Lux.

DEFAULTLIGHTING (Default lighting): A distant light that follows the view direction. This setting can be different per viewport.

  • 0: Default lighting is used if no other lights are switched ON.
  • 1: Default lighting is used instead of the light sources defined in the drawing.

LINEARCONTRAST (Linear contrast): Specifies the ambient light intensity. Values between -10 and 10 are accepted. A value of -10 results in maximum ambient light. A value of 10 results in no ambient light.

LINEARBRIGHTNESS (Linear brightness): Specifies a scaling factor for the light intensity. Values between -10 and 10 are accepted. The default value is 0 (no scaling). Negative values decrease the light intensity, positive values increase the light intensity. This setting can be different per viewport.

LIGHTGLYPHDISPLAY (Light glyph display): Controls the display of light glyphs.

FBXEXPORTLIGHTS (Fbx Export Lights): Specifies whether to export lights from model space.

General properties

The general properties are common to all lights:

  • Name: specifies a name for the light.
  • Type: specifies 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 increases performance.
  • Intensity factor: multiplies the Lamp Intensity property, the result is the Resulting Intensity.
  • Filter color: specifies the color of the light.
  • Plot glyph: if on, the light glyph is plotted.
  • Glyph display: controls the display of the light glyph.

Photometric light properties

LIGHTINGUNITS = 1 (American units) or 2 (International units).

  • 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.
    color temperatures lamp color list
  • 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, spotlights 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:
    • 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, the light is half as strong; at a distance of 4 units, the 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, the light is one quarter as strong; at a distance of 4 units, the 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.
No attenuation Inverse linear attenuation Inverse square attenuation
  • The Attenuation properties apply to generic lights only (LIGHTINGUNITS = 0).
  • Inverse square attenuation is applied automatically for photometric lights ( LIGHTINGUNITS = 1 or 2).

Rendered shadow details

  • Type: Sets the shadow type.
    • Sharp (raytraced): generates sharp edged shadows.
    • Shadow map (unsupported, using sharp): not supported
      • Map size: specifies the amount of memory for shadow calculation. Click the field, then select a value in the drop-down list (64/128/256/512/1024/2048/4096).
      • Softness: sets the softness of the shadow map. Enter a value between 1 and 10.
    • Soft (sampled): generates realistic shadows with soft edges.
      • Samples: sets the sampling size of the shadow
      • Visible in render: toggles the visibility in rendering
      • Shape: sets the shadow shape (linear. rectangle, disk, cylinder, sphere).

Spotlight hotspot and falloff properties

When a surface is illuminated by a spotlight, there is an area of maximum illumination (hotspot = 1) that is surrounded by an area of lesser intensity (falloff = 2).

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

Falloff angle: angle of the full light cone

Hotspot angle = 55, Falloff angle = 60 Hotspot angle = 30, Falloff angle = 60

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).

Managing Lights

The LIGHTLIST command opens the Drawing Explorer – Lights dialog box.

Here you can:

  • Create new lights.
  • Delete lights.
  • Select lights in the drawing.
  • Switch lights On/Off.

Defining a light

  1. Do one of the following:
    • Launch the LIGHT command.
    • Click the New () button on the Drawing Explorer – Lights dialog box.

      You are prompted: Enter light type [Point/Spot/Web/Distant] <Web>:

      Specify the light type.

    • Click a toolbutton on the Lights toolbar or the View or Visualize ribbon tab.
      • : spot light

      • : point light

      • : distant light

      • : web light

    You are prompted: Specify source position <0,0,0>:

  2. Specify a point in the drawing.

    You are prompted: Specify target position <0,0,-10>:

  3. Specify a point in the drawing.

    You are prompted: Enter an option to change: Name/Intensity factor/Status/Photometry/Hotspot/Falloff/Shadow/Attenuation/FilterColor/<eXit>:

  4. Specify the properties of the light.

  5. Choose Exit to conclude the command and create the light.

    A light glyph is displayed in the model, if LIGHTGLYPHDISPLAY = On.

Note: It is not possible to define web lights if LIGHTINGUNITS =0 (No lighting units).

Editing lights

Lights can be edited in the Properties panel.

  1. Do one of the following to select the light in the drawing:
    • Click the glyph of the light(s).
    • Select the light(s) in the Drawing Explorer – Lights, then right-click and choose Select lights in the drawing in the context menu.

    The properties of the selected light(s) appear in the Properties panel:

  2. Edit the properties.
  3. Press the Esc key to stop.

Defining the sun properties

  1. Launch the SUNPROPERTIES command.

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

  2. Edit the properties.
Note: When LIGHTINGUNITS = 1 or 2, the Color property of the sun cannot be edited.

Defining the geographic location

  1. Launch the GEOGRAPHICLOCATION command.

    The Geographic Location dialog box appears.

  2. (option) Check the Store geographic location information in drawing option.
  3. (option) Check the Use Map Grid coordinate system option.
  4. Do one of the following:
    • Type the latitude and longitude of the location in the Latitude and Longitude fields and select the appropriate hemisphere for each setting.
    • Click the Choose location... button, then select a city and timezone and click the OK button.
  5. (option) If you did not select a time zone in the previous step, choose a time zone in the Time Zones list.
  6. (option) Specify the Coordinates of the corresponding location in the drawing.
  7. Define the direction of the north.
  8. Click the OK button.