**Core Concept**
The visible spectrum of light refers to the range of electromagnetic radiation that is perceivable by the human eye, spanning approximately 380-780 nanometers (nm). This range includes the colors of the rainbow, from violet (shortest wavelength) to red (longest wavelength).

**Why the Correct Answer is Right**
The visible spectrum is a result of the way light interacts with the photoreceptors in the retina of the eye, specifically the rods and cones. The rods are sensitive to low light levels and are responsible for peripheral and night vision, while the cones are responsible for color vision and are sensitive to different wavelengths of light. The combination of signals from the different types of cones allows the brain to interpret the various colors within the visible spectrum.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultraviolet (UV) radiation has a shorter wavelength than the visible spectrum, typically below 380 nm, and is not perceivable by the human eye.
**Option B:** Infrared (IR) radiation has a longer wavelength than the visible spectrum, typically above 780 nm, and is not perceivable by the human eye.
**Option C:** Gamma rays have a much shorter wavelength than visible light, typically below 10 nm, and are not perceivable by the human eye.

**Clinical Pearl / High-Yield Fact**
Remember that the visible spectrum is just one small part of the larger electromagnetic spectrum, which includes forms of radiation that are not perceivable by the human eye, such as X-rays and gamma rays.

**Correct Answer: D. The visible spectrum of light spans approximately 380-780 nanometers (nm).**