Q Light object

Note: if you want light quickly in a scene, try the Camera Light.

What is a Light ?

A Light is required to illuminate a scene. Surfaces in the 3D scene will not be visible unless lit, or it emits light (set by the Shader's emissive color).

A Light has a color, which is blended with the surfaces' diffuse color. Be careful when using this - e.g. a surface with a pure red diffuse color will appear black when lit with a blue light as it will not reflect any blue light.

A Light has a radius; only surfaces within the radius will be lit. It also has an intensity (brightness) which reduces as you get further from the Light. The Light intensity is determined by 3 parameters:

1. the radius R. The intensity is 0 further from the light than the radius.
2. the Intensity at the origin I_O. The light intensity is never greater than 1. Setting the intensity at the origin greater than one will extend the bright spot of the light.
3. the Intensity at the radius I_R.

The light intensity then given by:

where

This can be seen more easily by plotting the Light intensity against radius for different sets of values:

R=25, Intensity O=6, Intensity R=0.1

The IntensityO value of 6 is greater than 1, and therefore extends the light hotspot out from the origin

R=25, Intensity O=1, Intensity R=0.1

The IntensityO value is changed to 1 in this example, notice how the hotspot is now localised to the origin.

You can use the lightcalc spreadsheet to view different effects, or better yet, try them in QStudio.

Omni and Spot lights

Two different types of light are supported in QStudio

• omni-directional. These lights illuminate uniformly in all directions.
• spot lights. These lights illuminate within a cone.

Spot light illumination is defined by a cone governed by 3 parameters:

• the orientation of the Group that the spot light is Instanced to.
• the minAngle of the cone. The light intensity is bright and constant from the axis of the cone to the minAngle.
• the maxAngle of the cone. The light intensity falls off from the minAngle to the maxAngle. No light is present outside the cone defined by maxAngle.

What can I do with a Light ?

In QStudio you can:

• create, duplicate and destroy Lights
• Instance them into a scene
• view or edit their properties

• view light limit data.

If you just want a temporary light, you can easily place one on the active camera.

Creating and Destroying Lights

If at least one Q file has been opened read-write then a Light can be created by:

• Duplicating a Light in the Tree view; right-click on the item and choose Duplicate.
• Create a new Light (shown below). Select the Lights warehouse, then right-click and choose Create Light. QStudio will then prompt for the name of the new Light (shown below). The Light will then be created and the properties dialog shown.
• Create a new Light from within the Instance prerequisites dialog.

A Light can only be deleted if it is not being used by any Instances. Select Delete from the Light's context menu to do this.

Light properties

The Light properties can be viewed or modified (if read-write) by:

• right-clicking on the Light in the Tree view and select Properties
• clicking the Properties button in the Instance properties dialog (if this light is instanced).

Capabilities properties

see here for details.

Color and Intensity properties

Color: this color picker widget sets the light color as discussed above.

Radius: this scaled slider widget sets the light's radius of effect in metres.

Intensity at Source: this scaled slider widget sets the light's intensity at its origin.

Intensity at Radius: this scaled slider widget sets the light's intensity at its cutoff point.

Angle properties

This tab defines spotlight properties and also determines whether a light is and omni light or spotlight. An omni light will have both angles set to 0.

Inner/Outer spot angle: these scaled slider widgets vary the spot light angles.

Marking a Light

When an Instance of a Light is marked the origin of the Light is marked with a wire-frame cube. The cube is the same size for all lights. The edges of the cube will always be displayed in the same color (purple in this case). The faces of the cube are colored the same color as the Light:

the colors and size of the marker can be changed by using the Visualisation Preferences.