To give an easy visualization for most people (average Americans, really, because most other people in the world already know what a meter looks like), imagine that the average doorknob is about 1m above the floor, so imagine basically the bottom part of a typical interior door is about 1m sq. Now, make a square out of 18 of those pieces wide by 18 pieces high.

Whoops, I overcooked my last minute edits while almost asleep. Yeah, I'm was off by 18x there.

For Americans: this is roughly 3500 sqft.

So very roughly a 300kW spotlight pointed at a relatively small area (wild guess at around 1km^2, anyone done the maths?)

Edit: A 5km diameter spot illuminated from 600km altitude.