Hi MXB300,
Welcome to pprune.
Your two questions are typical of "exams" and "studying": ie not really relevant, at least in the way they are typically asked.
To treat the "heavy" one first: what people want you to know is that:
1. Induced drag (sometimes known as lift-induced drag) is directly proportional to lift. So, increase lift, increase induced drag.
2. To get more lift on a wing, you either have to fly faster (and get more air over it) or if you fly slower, then you get less air over it, so that air has to be used more efficiently. To do this, you increase the angle of attack of the wing.
3. As you increase the angle of attack, the lift-induced drag - ie wing vortices - increases.
4. Those vortices are the main contributor to wake turbulence.
So, a heavy aircraft "clean" will actually have to have a higher angle of attack to generate lift. So create more turbulence.
Now, you may ask, when might you get in a situation at your local airfield where a heavy is going to fly by "clean". And if you do, you are probably at an airfield where there is a tower with full ATC. And if there is, they will have separation minima which they will make you hold for.
So to me, the point of the question is to explore lift/drag etc, and not a "real world" this is what to do answer.
As for lights.
The Air Pilot does say you can fly into Glasgow International without a radio! No-one has done that for decades! I doubt Glasgow even has light signals, but could be wrong.
I know at another, smaller, licensed Scottish airfield, the Health and Safety said it was too dangerous to have batteries in the control tower. So they would have to be stored downstairs in a vented cupboard. Or why couldn't the light just be plugged in? Of course, the point for the airfield having batteries was if the power went off!
The answer there was that they have hand-helds, the fire truck has a radio and they allow non-radio traffic anyway. So if the aircraft radio fails, not an issue either.
As to light signals working, read the Flight of the Gin Fizz - a deaf US pilot following in Calbraith Rodgers first trans-continental flight route. Basically, being deaf he couldn't hear the radio. Even after contracting many airfields and being told they would use lights, he never saw the lights most times. Sometimes, airfields that said they had lights, didn't!
Me, if non-radio I would rather look out for other traffic than for non-existent lights!