Importance

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Abstract

A level of received light detected by a light-receiving means (R) is given to both an indication controller (11) and a transmitter (13). The indication controller (11) obtains a flashing frequency corresponding to the given received light level, and flashes an LED (12) at the frequency obtained. The received light level transmitted from a transmitter (13) is demodulated and decoded in a receiver (4) and then given to an indication controller (3). The indication controller (3) obtains a flashing frequency corresponding to the given received light level, and flashes an LED (2) at the frequency obtained. Thus, the operator can recognize the received light level readily and reliably. Accordingly, it is only necessary for the operator to adjust the angle of the projecting optical system of a light-projecting means (T) in the vertical and horizontal directions so that the flashing frequency of the LED (2) lowers and eventually the LED (2) turns off, and to adjust the angle of the receiving optical system of a light-receiving means (R) in the vertical and horizontal directions so that the flashing frequency of the LED (12) lowers and eventually the LED (12) turns off.

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First Claim