shutter 30 produces a pulsed emission from a beacon . hot plate 40 radiates upward through openings 67 . shutter plate 52 slides to open and close the view of the hot plate . outer optical plate 38 has divergent and adjoining reflector openings 67 so that a large area source is seen when the shutter is open . means are also provided for urging the shutter into close engagement with the outer optical plate so that while in the open position the shutter plate is cooled so as not to become a radiator of energy when it is moved to the closed position .