What is the vergence of light that is parallel and originating from a distance of 20 feet or more?

The correct answer is zero vergence because light that is parallel, as would be the case for rays originating from a distance of 20 feet or more, is considered to have zero vergence. Vergence is a measure of the curvature of light rays; when light rays are parallel, they have no convergence towards or divergence away from a point, resulting in a vergence value of zero.

When light is coming from a distant source, such as 20 feet or more away, it effectively reaches the eye as parallel rays. This is a key principle in optics where distant objects create minimal curvature in light rays, maintaining a constant direction. As such, it is important for opticians to understand that the vergence of parallel light plays a crucial role in lens calculations and understanding vision correction.

Other ranges of vergence, such as positive or negative, represent light rays that converge to a point (positive) or diverge from a point (negative), which does not apply to light that is parallel. Infinite vergence typically refers to an idealized situation where rays would be considered at an infinite distance, but in practical terms, the appropriate classification for light from 20 feet away is zero vergence given the definition of parallel light.