Most luminescence dating methods rely on the assumption that the mineral grains were sufficiently "bleached" at the time of the event being dated.
For example, in quartz a short daylight exposure in the range of 1–100 seconds before burial is sufficient to effectively “reset” the OSL dating clock.
The older the sample is, the more light it emits, up to a saturation limit.
The minerals that are measured are usually either quartz or potassium feldspar sand-sized grains, or unseparated silt-sized grains.
This is usually, but not always, the case with aeolian deposits, such as sand dunes and loess, and some water-laid deposits.
Thermoluminescence dating (TL) is the determination, by means of measuring the accumulated radiation dose, of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments).It uses various methods to stimulate and measure luminescence.It includes techniques such as optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), and thermoluminescence dating (TL).These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar.The radiation causes charge to remain within the grains in structurally unstable "electron traps".As a crystalline material is heated during measurements, the process of thermoluminescence starts.