Which factor affects the performance and efficiency of an electric lamp?

The performance and efficiency of an electric lamp can be significantly impacted by both ambient temperature and the presence of dust and dirt. Ambient temperature is crucial because it influences the operating temperature of the lamp, which can alter electrical resistance and the luminosity produced. For example, higher temperatures can lead to reduced efficacy and shorter lifespan, while extremely low temperatures may hinder proper operation.

Additionally, dust and dirt can obstruct the light emitted by the lamp, reducing brightness and efficiency. When a lamp's surface is coated with debris, less light is transmitted, which can result in the need for higher wattage to achieve the desired illumination level. This not only diminishes the overall performance of the lamp but also leads to greater energy consumption.

Given these factors, it is clear that both ambient temperature and the presence of dust and dirt play a significant role in determining how effectively and efficiently an electric lamp operates. Thus, the correct answer encompasses the importance of both elements in assessing lamp performance.