**Core Concept**
The detection of light by the retina involves the conversion of photons into electrical signals. This process is mediated by the visual pigment rhodopsin in rod cells and cone cells. The minimum amount of light required for detection is related to the quantum efficiency of these photopigments.

**Why the Correct Answer is Right**
The correct answer is 1 photon. The detection of light by the retina is a quantum phenomenon, and the minimum amount of light required for detection is the absorption of a single photon by a rhodopsin molecule. This photon triggers a conformational change in the rhodopsin molecule, leading to the activation of a G-protein coupled receptor and the subsequent generation of an electrical signal. The quantum efficiency of rhodopsin is approximately 6%, meaning that 6% of absorbed photons result in a detectable signal.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it implies a threshold of multiple photons, which is not supported by the quantum nature of light detection.
**Option B:** This option is incorrect because it implies a threshold of light intensity, rather than the number of photons. While it is true that increasing the intensity of light will increase the number of photons absorbed, the minimum amount of light required for detection is still a single photon.
**Option C:** This option is incorrect because it implies a threshold of light duration, rather than the number of photons. The duration of light exposure does not affect the minimum amount of light required for detection.

**Clinical Pearl / High-Yield Fact**
The quantum nature of light detection is a critical aspect of visual physiology, and understanding this concept is essential for appreciating the mechanisms of visual disorders such as night blindness.

**Correct Answer:** 1 photon.