But then we remembered that we got new type of fluorescent lamps some month ago: they are high efficient and work with electronic ballasts at frequencies of 20...30 kHz.

And I rembered that technicians told me about same problem in hospitals, but only some times; now I understand.

Another reason for same problem we met at rescue stations: they are protected against burglary with system of IR emitters and receivers, and it's easy to guess what type F makes when IrDA is activated.....