Oil Lamp question

[Bananper]

When i was out riding the other day, my oil lamp on the dash started lighting up when i was on my way up a hilltop. I looked at my oil tank, and i could see that it was only halfways topped up with oil. I then filled it up, and the oil lamp wasn't lighting in the uphills anymore. So my question is: what makes the oil lamp light up? Is It because the engine doesn't get oil, or is there some sort of sensor that figures out that there's not much oil left?

(I know that this was NOT written very well, but I don't know how else to put it)

Thanks for any answers

[oldman]

There is a float on the sensor stem in oil tank that activates oil light when oil level falls to predetermined level

[Minia]

What oldman said. But it shouldn't turn on halfway... my oil light turns on at about 1/4 or 1/5 left of the tank.

[Jens Eskildsen]

A broken connection will also light it up as recall. (safety feature)