The BBC transmissions from Alexandra Palace whose eightieth anniversary we are celebrating this month are described as the first high-definition public television broadcasts. This is to distinguish them from rather cruder pictures demonstrated by public broadcasters on the continent, as this excerpt from BFI Screenonline makes clear:
The new BBC Television Service had begun. Widely regarded as the first high-definition television service in the world, the truth of this description depends on your definition of 'high definition'. It is usually said to be at least 240 lines and at least 25 images per second - the definition of the BTL [Baird] system of the time. Unfortunately, the BBC, in a publication the previous year, had told how "Herr Eugen Hadamovsky, Director-General of the German Broadcasting Service, opened the world's first regular high-definition television service on Friday, 22 March" . The German system was 180-line, not so different from BTL's 240. However, the 405-line, 50-field interlaced performance of the Marconi-EMI system was a tremendous advance in comparison, and in this regard there is no doubt that Britain led the world in high-definition television. By contrast, the USA had no regular television services at this time, though numerous tests had been broadcast using low-definition mechanical scanning, and NBC was planning an electronic system with over 300 lines; the Soviet Union was running a regular service - but it was 30-line with whirling discs - and in France there were tests of 180-line, 25-frame mechanical scanning.
Now standard television has left 405 lines behind and high-definition has different parameters.