What's the light curtain? Somebody maybe will ask this question when they are looking at this word. It's the new component of Iphone4? It's the new display of 3D movies? No, either wrong.

   Light curtains are opto-electronic devices that are used to safeguard personnel in the vicinity of moving machinery with the potential to cause harm such as (but not limited to) presses, winders and palletisers. Light curtains can be used as an alternative to mechanical barriers and other forms of traditional machine guarding. By reducing the need for physical guards and barriers, light curtains can increase the maintainability of the equipment they are guarding. The operability and efficiency of machinery can also be improved by the use of light curtains by, for example, allowing easier access for semi-automatic procedures.

The application in task: