PPT cameras track infrared (IR) light emitted from PPT markers. Infrared light from non-marker sources renders tracking unreliable or impossible. Thus, the tracked workspace should be lit by "cool" light sources (such as fluorescent or xenon lights) that do not generate IR light.  

Common infrared contamination sources

• Windows: Completely block outdoor light from the room's windows. Standard curtains and venetian blinds are usually not sufficient as they let through too much IR light. Use a high-quality block-out plastic or felt drape to achieve full light blockage.
• Incandescent (tungsten) light bulbs: Turn off all warm light sources and only use fluorescent light to illuminate your workspace during tracking.
• Some computer monitors and status lights: Some computer monitors and status lights on electronic devices emit IR.  Use the large camera view when troubleshooting for interfering light sources.  
• Reflective surfaces: Sometimes a surface reflects a warm light source that would otherwise not be in the field of view of the PPT cameras (e.g., a ceiling light reflecting off a chrome chair). Even the glass surface of a widescreen TV or the enamel surface of a white-board can be reflective enough to interfere.

Light leaking into your workspace?

If tracking is poor or calibration fails, check for light contamination:

1. Turn off all of your PPT markers.
2. Look at each camera's 2D view. If any show a cross-hair, then there is stray light.
3. Often it is a good idea to raise a camera's sensitivity to better detect stray light of this sort (lowering sensitivity after the problem light has been resolved).   

Always control ambient lighting?

Yes, every time you use your PPT system you will need to eliminate infrared light contamination. This includes during calibration and normal tracking.