Creating Light Sources

All light source cells are placed, by default, on the “Default” level. As well, they are made from Construction class elements. Thus, to avoid the elements appearing in your rendered view or image, you must “hide” them either by turning off the Default level, or by turning off Constructions for the view, prior to rendering. This setting is located in the View Attributes dialog box (Settings menu > View Attributes). When creating a light source, you must give it a name. While a default name, such as Point Light, Point Light (1), and so on, is provided by the system, it is good practice to give light sources more meaningful names. These names, which will appear in the Light List of the Define Light tool's dialog box, can be used to easily identify the light source if you want to modify any of its settings.

Placement scale of light source cells

Lighting in an image is not affected by the scale of the light source cells for Point, Spot, or Distant Lights. They merely define where the lighting is coming from and/or the direction.

By default, the Cell Scale setting for light source cells is set to 1. If necessary, you can change the Cell Scale setting to make your light source cells bigger/smaller. Subsequently, the last scale value input will be used for further light source placement during the session.

When you first use the Define Light tool during a session in a DGN file, the default values are displayed in the tool's dialog box. Any changes you make to the settings, when creating new light sources, or editing existing lights, will remain for the current session. When you exit the DGN, the settings revert back to the defaults.

Area Light source sizes

Unlike the Distant, Point, and Spot light source cells, the size of an Area light source is defined by the element (convex polygon) being used to create it. The size of the element, and therefore the light source, affects the rendered image when ray tracing, radiosity solving, or particle tracing is used. When constant, smooth (Gouraud), or Phong shading is used, however, the size of area light sources has no effect.

Creating Point Light sources

Similar to a light bulb, light radiates in all directions from a Point Light source. These light sources do not cast shadows when used with Phong rendering. To create a Point Light source, normally you need only define its location. Where an IES lighting file is specified for a Point light source, the direction that light radiates may vary, and you may be required to define a direction.

To ensure that the IES values are applied correctly to the light source, it is recommended that Point Lights be used with IES data. Using Spot Lights or Area Lights can result in restriction of the IES lighting to within the cone of spotlights, or to the front side of area lights.

Point Light source cell.

See To create a Point light source .

Creating Spot Light sources

Working like a real spot light, settings for the Spot Light sources let you focus the beam (Cone Angle), and the edge fall-off, where the light falls from full intensity to zero (Delta Angle).

To create a Spot Light source, you define first the location of the light source, and then the target point. The Distance value (for attenuation, if on) is set by default to equal the length of the cone as the light source is placed — that is, the distance between the light source and the target point.

For Radiosity Solving, and Particle Tracing solutions, the Distance setting is ignored. In these cases the lights attenuate according to the square of the distance.

Spot Light source cell.

See To create a Spot light source .

Creating Distant Light sources

Only the direction of Distant light sources is important, as they provide similar lighting to sunlight. No matter where in the design you create a Distant light source, all surfaces facing that direction are equally illuminated. In creating a Distant Light source, you define first the location of the light source, and then its direction.

Distant Lights, if pointing upward and turned on, behave differently in the various rendering modes, as follows:

• Constant, Smooth, and Phong — Distant Light sources always will shine.

• Particle Tracing — A Distant Light source is presumed to be a realistic representation of a sun and is considered off if pointing upward (similar to the Sun being below the horizon).

• Radiosity — As with particle tracing, a Distant Light is presumed to be a realistic representation of a sun, and is considered off when pointing upward if: Light Interpretation is set to Extended (the default), or Add Sky Light to all Solar and Distant Lights is on. Otherwise, upward-pointing Distant lighting will shine.

• Ray tracing — As with particle tracing, a Distant light is presumed to be a realistic representation of a sun, and is considered off when pointing upward if Add Sky Light to all Solar and Distant Lights is on. Otherwise, upward-pointing distant lighting will shine.

By default the Intensity of a Distant light source is defined as 1.0 and is equivalent to the intensity of the sun at the brightest point on Earth, on the brightest day when the sun is directly overhead (120,000 lumens per square meter). In contrast, for a scene requiring an overcast day, you might, for example, have a distant light with an intensity of 0.001.

To simulate the yellowish color of sunlight at high angles, you can set the light source Color to the following RGB values: 255, 247, 235 (or, on a scale of 0 to 1, to 1.00, 0.97, 0.92). To simulate the more reddish color of sunlight at low angles, such as at sunset, decrease the Green and Blue values from those specified above.

Distant light source cell.

See To create a Distant light source .

Creating Area Light sources

Area Light sources are useful for simulating lighting such as that from fluorescent lighting. You can create an Area Light source from any existing convex polygon. That is, you first define a (polygonal) shape for the geometry. You then select Create in the Define Light tool, select the geometry, then define the direction that the area light “shines”.

Polygons used to create Area Light sources may have any number of vertices, but they must be convex polygons.

During processing, Area Light sources are first converted into triangular-shaped light sources. A rectangular Area Light source, for example, is converted into two triangular light sources, while a pentagon is converted into five triangular light sources, one for each edge.

If a radiosity solution is being computed, each (converted) triangular light source is processed separately. In a design containing only one rectangular light source, therefore, there will be shots for two light sources (one for each triangle).

Area Light sources have an additional setting, Samples, that is applicable only to ray tracing, including the ray traced display of radiosity and particle tracing solutions where Ray Trace Direct Illumination is enabled. The Samples setting affects how the light source is treated during ray tracing processing. The effects of the settings are most noticeable in the appearance of shadows cast by the Area Light source. Higher Samples values produce smoother shadows but take longer to process.

The size of the Area Light source also affects the appearance of shadows. Smaller Area Light sources may require fewer samples than larger ones to produce reasonable ray tracing results.

Left: Samples set to 4 (the default). Right: Samples set to 50 — shadows are much smoother.

See To create an Area Light source .

Creating Sky Openings

(Applicable only when using Ray Tracing, Radiosity, or Particle Tracing rendering modes). You can use Sky Openings to generate more efficient solutions for indoor scenes lit with Distant, Sky, or Solar light.

Sky Openings are not true lights in the traditional sense, but act as a control when using Solar, Distant, and Sky lights. Performance is improved by only testing for shadows in the directions of the sky openings, as opposed to testing the entire sky. You place a Sky Opening the same way that you place an Area Light. That is, you first define a (convex polygonal) shape for the geometry. You then select Create in the Define Light tool, select the geometry, then define the direction that the opening “shines” light. For example, an opening representing a window would point toward the inside of the room (that is, the direction the sunlight travels into the room from the window).

Polygons used to create Sky Openings may have any number of vertices, but they must be convex polygons.

When there are any Sky Openings that are ON in a design, Solar, Distant, and Sky light will shine through those openings only, thus reducing the amount of time spent calculating light energy/particles outside the scene. Sky Openings apply even when shadows are OFF for the corresponding light. This means that you can model a room with one window, then use Solar and Sky light to illuminate the scene through that window only, without calculating shadows.

Sky Openings provide the greatest benefit when using Sky light. Without Sky Openings you need to have “Sky samples” set to a very large number in order to get reasonable shadows. With Sky Openings enabled, the “Sky samples” are considered only for that light shining through the sky opening and does not affect performance much.

If Sky Openings are enabled, we recommend that “Sky samples” be set to a value of at least 145. Often, for ray tracing and radiosity solving, a much higher value will be required. This applies also to radiosity solving and particle tracing, when Ray Trace Direct Illumination is enabled.

When computing shadows from Sky Openings, for Ray Trace, or Ray Trace Direct Illumination, the distance from the opening determines the number of shadows samples taken. When a point is very far from the opening, it can only see a small portion of the sky, and only “Min Samples” (defined in the Sky Opening) are taken. As points closer to the opening are illuminated, those points can see more of the sky and the number of shadow samples will increase, up to “Max Samples”.

When using Sky Openings, it is highly recommended that “Jitter sky samples” be turned on. This will reduce many artifacts that can occur from sky shadows.

Note that only objects in front of the sky opening will receive light and, as with a real window, objects outside (behind) the opening can cast shadows through the opening. Also keep in mind that you do not need to create an opening for every pane of a window; you can create a single opening that covers all the panes, or even a group of windows. The Sky Opening is merely an efficiency tool, but there are trade-offs — the more openings you have, the more processing time required; fewer but larger openings, however, could require more shadow samples to achieve good results. See To Create a Sky Opening.