In paragraph 3, what does the narrator mean when he uses the word enlightening?

When the narrator uses the word enlightening in the third paragraph, he is about to recount the story of shooting the elephant. What he means by enlightening is that he learned the truth about the true nature of imperialism.
The narrator is confronted with an elephant that had been rampaging and had killed a native. The elephant is now calm and no threat to anyone. Nevertheless, the narrator is part of the ruling class police force and is being followed by a crowd of Burmese curious to see him put on show. Though he knows it is both cruel and pointless, with the crowd watching the narrator feels forced to shoot the elephant. He knows it is senseless, but he also knows he will lose face and look foolish if he does not kill the animal.
He writes that :

it was at this moment, as I stood there with the rifle in my hands, that I first grasped the hollowness, the futility of the white man's dominion in the East.

He is enlightened (taught) by this episode that he is no more than a "puppet" playing a role. He may look powerful but he is not, because he has to behave in a pre-programmed way in order to keep the respect of the natives, even if that means acting against his reason and his nature.