## Core Concept
The question pertains to the minimum illumination required for satisfactory vision, which is a concept within the realm of ophthalmology and visual physiology. It involves understanding the sensitivity of the human eye to different levels of light.

## Why the Correct Answer is Right
The correct answer, 50-100 lux, is considered the minimum illumination required for tasks that require some visual detail, such as reading or other everyday activities. This level of illumination ensures that the visual acuity and comfort are optimized for such tasks. The eye's photoreceptors, including rods and cones, function optimally within this range, allowing for clear vision and minimal eye strain.

## Why Each Wrong Option is Incorrect
- **Option A:** 10-20 lux is too low for satisfactory vision for tasks requiring detail, as it may lead to significant visual strain and decreased acuity.
- **Option B:** 200-500 lux is higher than the minimum required for satisfactory vision and is often recommended for tasks requiring high visual acuity or detailed work.
- **Option D:** 1000-2000 lux is excessively high and can cause discomfort or glare, especially for prolonged visual tasks.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the recommended illumination levels can vary based on the task's visual demands. For example, reading and detailed work often require 50-100 lux, while tasks requiring less visual detail might be adequately supported by lower illumination levels.

## Correct Answer: C. 50-100 lux