Abstract: A head unit for remote light sensing utilizes a lens secured in one end opening proximate to the light to be sensed, as well as a passive light source having a radiating end and a passive light collector having a receiving end, the source and collector being secured in a second opening such that both are substantially adjacent to the focal point of the lens and to each other such that the lens substantially collimates light emitted from the passive light source, and focuses received external collimated light at the focal point of the lens. The passive light source and passive light collector are respectively connectible to a powered light source and a photoelectric detector.