Most commonly used colour of the filter used in dark room safelight is:
**Core Concept**
In a darkroom, a safelight is used to illuminate the area while minimizing exposure to light-sensitive materials. The filter used in a safelight is designed to allow a specific range of light wavelengths to pass through while blocking others.
**Why the Correct Answer is Right**
The most commonly used colour of the filter in a darkroom safelight is red, specifically a red #2 or red #5 filter. This is because red light has a longer wavelength (approximately 620-750 nanometers) and is less likely to cause exposure to light-sensitive materials such as film or photographic paper. The red filter blocks blue and violet light, which are more energetic and can cause exposure.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not specified, but other colours such as green or yellow are not typically used in darkroom safelights because they do not effectively block blue and violet light.
* **Option B:** This option is not specified, but other colours such as blue or violet are not used in darkroom safelights because they can cause exposure to light-sensitive materials.
* **Option C:** This option is not specified, but other colours such as amber or orange may be used in certain applications, but are not the most commonly used colour in darkroom safelights.
**Clinical Pearl / High-Yield Fact**
When working in a darkroom, it's essential to use a safelight with a red filter to prevent exposure to light-sensitive materials. This is a critical step in ensuring the quality and integrity of photographic prints.
**Correct Answer: A. Red.**