Suppressive fire usually achieves its effect by threatening casualties to individuals who expose themselves to it. Willingness to expose themselves varies depending on the morale, motivation and leadership of the target troops. Suppressive fire is often used as covering fire, defined by NATO as "Fire used to protect troops when they are within range of enemy small arms." This is sometimes called "winning the firefight" in an infantry-only action. However, suppressive fire may be used against indirect firers, enemy air defenses or other military activities such as construction work or logistic activities, or to deny an area to the enemy for a short period of time (it is unsuitable for prolonged area denial due to ammunition supply constraints). Using smoke to 'blind' enemy observation is a form of non-lethal suppression and at night illuminating flares may be used to suppress enemy activities by denying them the cover of darkness.