On the view windows, the point light looks like this: | ![]() |
The point light dialogue box is shown on the right: Click on the Color box the alter the light's colour. This brings up a dialogue allowing Hue/Saturation/Value (HSV), Red/Green/Blue (RGB) or Hue/Lightness/Saturation (HLS) values to be set to define the light colour. The Intensity, I0, of the light is simply how bright it is. By default, this set to 1. The intensity of this light at any point in space, I(r), is a function of this value, the Decay Rate, d, and the distance from the light source, r as follows: I(r)= I0/(1+dr+(dr)2) Close to the light (r<<1/d) the intensity is approximately constant. Far from the light (r>>1/d), it follows an inverse square law (i.e. decays as 1/r^2) as shown in the plot below for a range of decay rates: |
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The Intensity of a light source can be negative. In this case, it becomes a source of 'darkness' which,
although physically unrealistic, can be a useful effect. The Decay Rate defines the drop off in the intensity of the light per unit distance from the light. A high value means that the light will be bright only very near to the light source, while a small value means it only drops off a little. A value of 0 causes the light to be the same brightness everywhere. |
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Directional lights are useful for simulating light sources which are far away, the most obvious
example being the sun. Light from the sun is virtually parallel because of the tiny angle
subtended even across the whole Earth's diameter. Also intensity does not drop off over noticeably
as the Earth's diameter is small compared with the distance the light has already travelled. To create a directional light, either click on the light icon and then click its position on a viewport and drag in the required direction (if you do not drag, you will end up with a point light), or select Object -> Create Primitive -> Directional Light and enter the position and orientation as prompted. |
Because of their inherent simplicity, the editing dialogue box brought up by double-clicking
the light on the Object List or via the Edit menu, allows only 2 parameters to be
specified: Color - allows the light's colour to be specified with the usual 3 HSV/RGB/HLS bars. Intensity - allows the brightness to be specified. This value is independent of position. |
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Spotlights look like this when displayed in the view windows: This clearly shows the orientation of the emitted light beam. |
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Once created, spotlights can be edited either by double-clicking
on the light in the Object List or be selecting the object and clicking on Edit -> Edit Object.
This brings up a dialogue box like this: Cone angle is the extent of the beam spread. A small value produces a narrow beam. Falloff rate defines how quickly the light fades as we move radially outwards from the centre of the beam. A value of 0 means there is no falloff and the light will therefore be of uniform intensity right to the edge of the beam beyond which it will be zero. Radius is the physical size of the light which affects rendering with soft shadows switched on (see Rendering). Intensity and Decay Rate are as defined for Point Lights. |
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The first thing to do is to create the object you want to represent the light source. The image on the right is an example of a 'bulb' which was created by applying the lathe tool to a curve. The rendered image shows the bulb 'turned off'. | ![]() |
To make it into a light source, we need to put a light source inside it. The point light source is
the best type for this purpose. Having positioned the light in the bulb, you will need to make the bulb
transparent so that the light can escape and, thus, interact with its surroundings. Alter the transparency
in the texture to achieve this. The light will now shine out from the object but the object itself will not 'glow' and so will not look realistic. To get this effect, add some emissive colour to the object. Alter the diffuse and emissive colours to get the right effect and make sure the overall colour matches that from the light. The image on the right shows the results of these changes. Note that 'soft shadows' had to be switched on otherwise artefacts can appear when light sources are placed inside objects. |
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Another example of 'realistic' lighting is shown on the right. The 'lights' are cylinders with point light sources positioned within: | ![]() |
![]() perspective view of set up for 'cookie' scene. The screen on the left has the cookie image set for a transparency map and is projected onto right hand screen at which camera is pointing. |
![]() binary image map created in 2D graphics program. |