What does an infrared (IR) filter block?

An infrared (IR) filter specifically blocks infrared light while allowing visible light to pass through. This type of filter is designed to separate infrared wavelengths from the visible spectrum, which is essential for certain photographic techniques.

When using an infrared filter, photographers can capture images that highlight the differences in how infrared light interacts with various materials. Intriguingly, foliage often appears bright in IR photography due to its high reflectance of infrared rays, while other elements in the scene can take on very different appearances compared to standard visible light photography.

The other options are not applicable in this context: ultraviolet light is typically blocked by UV filters, visible light refers to the range of light humans can see, and X-rays are a completely different part of the electromagnetic spectrum that infrared filters do not interact with. Thus, the main function of an infrared filter is to selectively filter out infrared light, allowing for creative and unique photographic outcomes.