Vapour trails and lights

Hi all
Whilst in tenerife we had an apartment which looked upon the flightpath into tfs. Out of interest is there an international standard on how the lights on an aircraft should flash or are they just randomised?
Also on the way out and back I noticed the engines were producing a vapour trail. What actually causes this as I have noticed on some aircraft trails don’t appear ans some they do. No doubt it has something to do with the weather conditions? :confused:

Take a look here: http://www.aerospaceweb.org/question/electronics/q0263.shtml

I presume the vapor you are talking about is a contrail – An artificial cloud created by an aircraft; caused either by condensation due to the reduction in air pressure above the wing surface or by water vapor in the engine exhaust)

The wingtip strobes on a Boeing flash once, the wingtip strobes on an Airbus flash twice.

Not sure of any laws governing other lights such as Anti Collision Beacons and so on.

As far as Vapourtrails/contrails, there is heaps of info on the Net covering their formation. There are so many variables as to how long they stay around for. What you see in the sky is hot exhaust gas condensing in the very cold air (-50/-60), similar to when you exhale on a freezing cold winters day.