According to this article, there are about 10 different types of external lights on airliners these days. The ones that you notice are probably landing lights. I was looking out of one of my roof skylights on Saturday evening when it was particularly clear and I could see 8 aircraft at a time. I noticed then that the landing lights were switched on quite early, when the planes were still descending across North London before joining the runway approach over Docklands. I don't know whether the extra and brighter lights are imposed by the authorities or just offered as a feature by manufacturers (in the same way that Mercedes have brighter lights than Vauxhall).
Richard Jennings ● 6815d