**Core Concept**
The mean radiant temperature (MRT) is a measure of the temperature of an environment, taking into account the temperature of objects within that space. It is an important factor in heat transfer and can contribute to thermal comfort or discomfort. MRT is particularly relevant in occupational health, environmental science, and building design.

**Why the Correct Answer is Right**
The MRT is typically measured using an instrument called a globe thermometer. This device consists of a blackened metal sphere that is exposed to the environment, allowing it to absorb radiation from surrounding objects. The temperature of the sphere is then measured, providing an estimate of the MRT. The globe thermometer is a simple yet effective tool for assessing the thermal environment, and its use is widely accepted in various fields.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a correct option, as the question is asking for a device or method used to measure MRT, not a type of temperature.
* **Option B:** This option is incorrect because it does not specify a device or method used to measure MRT.
* **Option C:** This option is incorrect because it is not a recognized device or method used to measure MRT.

**Clinical Pearl / High-Yield Fact**
It is essential to consider the MRT when designing buildings or working in environments with high temperatures, as it can significantly impact thermal comfort and even contribute to heat-related illnesses. A good rule of thumb is to maintain an MRT of at least 20°C (68°F) in indoor environments to ensure thermal comfort.

**Correct Answer: C. Globe thermometer.**