## Core Concept
The human eye can perceive a specific range of wavelengths within the electromagnetic spectrum, which is referred to as visible light. This range allows us to see different colors. The visible spectrum is bounded by the ultraviolet (UV) and infrared (IR) regions, which are not visible to the human eye.

## Why the Correct Answer is Right
The correct range of the visible spectrum for the human eye is approximately 400-700 nanometers (nm). This range includes all the colors of the rainbow, from violet (around 400 nm) to red (around 700 nm). The mechanism behind our ability to see this range involves the structure of the eye, particularly the lens and retina, which are sensitive to these wavelengths. Photoreceptor cells in the retina, such as rods and cones, convert light within this spectrum into electrical signals that are interpreted by the brain.

## Why Each Wrong Option is Incorrect
- **Option A:** Less than 400 nm refers to the ultraviolet (UV) part of the spectrum, which is not visible to the human eye. UV light can cause damage to the eye but is not perceived as visible light.
- **Option B:** More than 700 nm refers to the infrared (IR) part of the spectrum, which is also not visible to the human eye. IR radiation is felt as heat rather than seen as light.
- **Option D:** A range that does not encompass 400-700 nm would either exclude parts of the visible spectrum or include non-visible parts, making it incorrect.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the visible spectrum of 400-700 nm is crucial for human vision. Conditions or diseases affecting the eye can alter perception of this spectrum, leading to visual impairments. For example, certain types of color blindness involve deficiencies in perceiving specific parts of this spectrum.

## Correct Answer: C. 400-700 nm.