How to Use Lights in BricsCAD

Quick answer: Good lighting is what makes a rendered scene feel realistic. BricsCAD supports point, spot, web, and distant lights, each with general, photometric, geometry, and attenuation properties, plus separate sun and geographic location settings.

The Lighting Glossary

• Ambient light: light from an unspecified source.
• Distant light: light from an infinitely far source, lighting the entire scene from the same direction.
• Fall-off: the decrease in brightness the farther you get from the light source.
• Point light: shines in all directions from a central point.
• Spot light: focusable light aimed at one area.
• Web light: approximates real-world light distribution using a 3D representation of light intensity; only creatable if LIGHTINGUNITS is set to 1 or 2, the same requirement covered on this hub’s rendering preferences page.
• Attenuation: the fall-off in brightness with distance.

Light System Variables

• LIGHTINGUNITS: 0 is generic lighting; this source describes it as an obsolete option that can no longer be set, though it may still exist in older drawings, worth noting that the rendering preferences page in this hub described this same value simply as “no lighting units are used” without that obsolescence note. 1 enables Photometric lighting with American units (Foot-Candles); 2 enables it with International units (Lux).
• DEFAULTLIGHTING: a distant light following the view direction, settable per viewport; 0 uses it only if no other lights are on, 1 uses it instead of the drawing’s defined light sources.
• LINEARCONTRAST (deprecated): sets ambient light intensity, -10 (maximum ambient) to 10 (none).
• LINEARBRIGHTNESS (deprecated): a light intensity scaling factor, -10 to 10, default 0, negative decreases and positive increases intensity, settable per viewport.
• LIGHTGLYPHDISPLAY: controls whether light glyphs display.
• FBXEXPORTLIGHTS: whether lights export from model space.

General Light Properties

Common to every light type: Name, Type (spot, point, web, or distant), On/Off, Shadows (turning them off improves performance), Intensity factor (multiplies Lamp Intensity to produce the Resulting Intensity), Filter color, Plot glyph, and Glyph display.

Photometric Light Properties

Available when LIGHTINGUNITS is 1 or 2:

• Lamp intensity: the light’s brightness, in candela (cd), the SI base unit of luminous intensity.
• Resulting intensity: Lamp intensity multiplied by the Intensity factor.
• Lamp color: the light’s inherent color, or its color temperature in Kelvin or standard values.
• Resulting color: the combination of Lamp color and Filter color.
• Photometric web: available for Web-type lights, alongside Web offsets, though not yet implemented.

Geometry Properties

Position (the light’s location), Target (for point, spot, and web lights), and Targeted (toggles the target property).

Attenuation Properties

In the real world, objects appear darker farther from a light source, and attenuation properties simulate this. An alternative is using limits, defining where a light starts and stops shining, which calculates illumination faster. Attenuation applies to spot and point lights only, not photometric lights.

• Type: None (distance has no effect), Inverse Linear (light is half as strong at 2 units, a quarter at 4), or Inverse Square (a quarter as strong at 2 units, a sixteenth at 4).
• Use Limits: set to Yes to activate Start limit offset and End limit offset, both measured from the light’s centre, defining where it starts and stops shining.

Attenuation properties apply to generic lights only (LIGHTINGUNITS = 0); Inverse Square attenuation applies automatically for photometric lights (LIGHTINGUNITS = 1 or 2).

Rendered Shadow Details

• Sharp (raytraced): sharp-edged shadows.
• Shadow map: not supported, falls back to Sharp.
• Soft (sampled): realistic soft-edged shadows, with Samples (sampling size), Visible in render (toggle), and Shape (linear, rectangle, disk, cylinder, or sphere).

Spotlight Hotspot and Falloff

A spotlight’s hotspot is the area of maximum illumination; falloff is the surrounding, less intense area. Hotspot angle defines the central light cone; Falloff angle defines the full light cone. The closer these two angles are, the sharper the light cone’s edge; the greater the difference, the softer the edge.

Managing Lights

LIGHTLIST opens the Drawing Explorer’s Lights dialog, where you can create new lights, delete them, select them in the drawing, and switch them on or off.

Defining a Light

1. Launch LIGHT (prompted for a type: Point, Spot, Web, or Distant, defaulting to Web), click New in the Drawing Explorer’s Lights dialog (same prompt), or click a tool button for spot, point, distant, or web light on the Lights toolbar or View/Visualize ribbon tab. You’re prompted for the source position.
2. Specify a point. You’re prompted for the target position.
3. Specify a point. You’re prompted to change Name, Intensity factor, Status, Photometry, Hotspot, Falloff, Shadow, Attenuation, or FilterColor, or exit.
4. Set the properties you want.
5. Choose Exit to create the light; its glyph displays if LIGHTGLYPHDISPLAY is on.

Web lights can’t be defined if LIGHTINGUNITS is 0.

Editing Lights

1. Select the light by clicking its glyph, or by selecting it in the Drawing Explorer’s Lights dialog, right-clicking, and choosing Select lights in the drawing.
2. Edit its properties in the Properties panel.
3. Press Esc to stop.

Defining the Sun Properties

1. Launch SUNPROPERTIES; the Drawing Explorer’s Lights dialog opens, showing the sun’s properties in the Editor panel.
2. Edit the properties.

With LIGHTINGUNITS set to 1 or 2, the sun’s Color property can’t be edited.

Defining the Geographic Location

1. Launch GEOGRAPHICLOCATION; the Geographic Location dialog opens.
2. Optionally tick Store geographic location information in drawing.
3. Optionally tick Use Map Grid coordinate system.
4. Either type the Latitude and Longitude directly (selecting the correct hemisphere for each), or click Choose location… and select a city and time zone.
5. If you didn’t choose a time zone in the previous step, choose one from the Time Zones list.
6. Optionally specify the drawing coordinates corresponding to that location.
7. Define the direction of north.
8. Click OK.

Frequently Asked Questions

Can I create a web light with generic (non-photometric) lighting units? No, LIGHTINGUNITS needs to be set to 1 or 2 first.

Does attenuation apply to photometric lights? No, attenuation properties apply only to generic lights; photometric lights use Inverse Square attenuation automatically.

Why can’t I edit the sun’s color property? Check LIGHTINGUNITS, with it set to 1 or 2, the sun’s Color property becomes locked.

What determines whether a spotlight’s edge looks sharp or soft? The difference between its Hotspot angle and Falloff angle, close together for a sharp edge, further apart for a softer one.