** When you buy products through the links on our site, we may earn a commission that supports NRA's mission to protect, preserve and defend the Second Amendment. **
Q: What do scope companies mean when they talk about “twilight factor”?
A: Twilight factor is a calculated number measuring low-light optical performance. It is obtained by multiplying the magnification of the optical system by the diameter of the objective lens in millimeters, and taking the square root of the product. In general, the higher the twilight factor number, the better the potential performance.
