What does a film badge or TLD measure during its period of use?

A film badge or Thermoluminescent Dosimeter (TLD) is designed to measure and record the total dose of radiation that a person is exposed to over a specific period of time while the device is worn. These dosimeters accumulate radiation exposure data, which allows for tracking the cumulative dose over days, weeks, or months, depending on how long they are worn. The response of the film or the TLD crystals to ionizing radiation provides a dose-reading after processing, reflecting the total exposure rather than just a snapshot of a single moment in time or event.

The other options don't accurately represent what a film badge or TLD does. For example, while they do record exposure, they are not designed to indicate current radiation levels at any given instant, nor do they specifically measure environmental radiation separately from personal exposure. Their use is primarily focused on personal dosimetry, making them essential tools in monitoring cumulative radiation exposure for workers in various fields involving radiation.