Temperature Range might be somewhat difficult to define, since you may have an upper and lower limit. We’ve seen consumer applications that need to survive from high temperature environments around 100°C, outside in the hot desert at 41°C, and other applications that need to function at -40°C. Space applications have a much wider temperature range, depending on sun exposure.
Then the next key is to determine what temperature to use in your simulation or calculations. We recommend using the highest temperature in your range first. If the simulations determine your heat sink cannot perform well enough in this case, then the heat sink is inadequate for your application.