Recently I changed ceiling lights in two rooms of my house. In order to install a Japanese type ceiling light, we need a one-touch adaptor on the ceiling (the following image).
Unfortunately an adaptor was not equipped in two rooms. I asked an electrical worker to install the adaptors, because installation should be done by a licenced worker.
It took one hour to install two adapters. Its cost was 5000 yen ($49.02 €35.46) for each, total 10000 yen ($98.04 €70.92).
