Let me suggest a simple but illuminating exercise for a time when you have absolutely nothing else to do. Take one school atlas and on a piece of tracing paper reproduce the tapering convolutions of the Amazon river in South America, complete with all its very many tributaries.
Then turn the resulting illustration on its side so that the mouth, where the river meets the sea, is at the top. Voila, you have before you a perfect representation of a complex lightning stroke.
The incandescent channel of air that comprises a lightning flash from a thundercloud to ground is no more than an inch or two in diameter. The path it follows is often "jagged" in appearance, as the electrical discharge zig-zags through the atmosphere, darting this way and that to find the electrical route of least resistance.
Sometimes, indeed, it cannot make up its mind and the stroke breaks up - with branches heading off in two or many more directions - to provide a multitude of incandescent Amazonian atmospheric tributaries.
A conspicuous feature of such a lightning flash is the flicker in the light that emanates from it.
The whole episode lasts for about a second, but its illumination is not constant; it consists of a number of separate strokes, each lasting a very short time and each following the other intermittently at intervals estimated to be about a 30th part of a second.
The most frequent number of individual strokes in a single flash is three, but as many as 47 have been recorded. Moreover, in the presence of wind, the lightning path may be blown sideways, so that successive strokes combine to produce the illusion we know as the phenomenon of "ribbon lightning".
A popular distinction is often made between "forked" and "sheet" lightning, but this is a distinction that contains no difference. The former is a stroke of lightning whose path is clearly visible; the latter is the diffuse glow that can be seen if the lightning flash itself is obscured by cloud or rain.
Lighting is usually intensely white in colour. When viewed through a curtain of rain, however, its colour is altered as the raindrops filter out the blue portion of the spectrum, making it appear a yellow or a reddish brown.
Occasionally, the appearance of a very distant flash is altered by the intervening atmosphere, so that red or rose-pink lightning can be seen. Even green flashes have been reported, though these are thought to be extremely rare.