Question

When Infrared Communication equipment is setup on the roof of the building, the residents around it may look at the beam through telescope or field glasses and the Infrared reception level may exceed the level at the output of the equipment because of the magnification of optical equipment. Is it probable that class 1 level at the output becomes class 2 level at the eye by using the telescope? Do you know the case of the trouble and the solution ?

Answer

This is the answer of the safety of the Infrared reception level based on the calculation.

Class 1 of the equipment means that the Infrared transmission level is safe even if we look at it through the naked eye or 50mmΦ telescope. Class 1 does not become class 2 even if telescope is used. Infrared Communication equipment must be safe when human looks at the beam including the reception point. In the case of Infrared Communication between buildings, human may not look at the beam on the transmission route and the Infrared power density at the reception point is examined now. If the beam of 10cmΦ at the transmission point expands to 1mΦ at the rooftop of the building 1km apart, the Infrared power density reduces to 1%. Even if it is class 3B at the transmission point, the reception level is class 1 at the reception point and the safety is possible to be guaranteed.

This is an example.

The Infrared power density at the reception point is adjusted to be class 1, actually the beam diameter is expanded. Accordingly it is safe even if field glasses is used. When telescope of 50cmΦ is used, the trouble may happen. But now the operator of the equipment only give attention to the manager of the setup point. The dangerous situation can be avoidable usually because the strong red light is visible though it is near Infrared and human will turn the eye away. Total output power of ordinary Infrared Communication equipment is at most 50mW and it does not hurt the eye even if human looks at the beam.

It is almost not possible that human looks at the beam on the transmission route. But it is possible that human looks at it behind the equipment. The safety is maintained even in this case from the viewpoint of the reduction of the reception power level.