Is being a light sleeper a medical condition?

Is there an element reflects light depending on condition?

• Is there a specific element or array of elements that reflect light depending on circumstances. For example a light shown from below an element simply passes through the element. However, once a light is shown from above the second light reflects off the surface due to the illumination below. The reflection of the bottom light would be irrelevant. In other words: Is it possible to build a light logic gate and does a logic gate for light already exist?

• Answer:

  No single element or simple mixture of elements can do this, but there are complex semiconductor devices called photonic switches that can do something similar to that which you describe. http://en.wikipedia.org/wiki/Optical_switch