Toggle Lights

$N$ people are standing in a line outside a dark tunnel. The tunnel has $2N$ light bulbs, numbered from $1$ to $2N$, all initially turned OFF. Each person enters the tunnel, one by one, and toggles the state of the some light bulbs. Specifically, the $i^{th}$ person toggles the state of all lights numbered $2ik$ such that $1 \leq 2ik \leq 2N$, where $k$ is any integer that satisfies the inequality