**Core Concept**
The Illuminating Engineer Society (IES) provides guidelines for recommended illumination levels based on various activities and environments. The IES recommends specific illumination levels to ensure optimal visual performance, comfort, and safety.

**Why the Correct Answer is Right**
The correct answer is based on the IES recommendation for general office work, which requires a moderate level of visual performance. The recommended illumination level is calculated to provide sufficient light for tasks such as reading and writing, without causing glare or discomfort. The IES takes into account factors such as the type of task, the age and health of the occupants, and the color and reflectance of the surroundings.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is too low for general office work, which requires a moderate level of visual performance.
* **Option B:** This option is incorrect because it is too high for general office work, which can cause glare and discomfort.
* **Option C:** This option is incorrect because it is not a valid illumination level recommended by the IES.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the IES recommends different illumination levels for various activities, such as reading (10-20 foot-lamberts), writing (5-10 foot-lamberts), and computer work (20-40 foot-lamberts). Understanding these recommendations can help designers and architects create visually comfortable and productive environments.

**Correct Answer:** 500 lux.