is important. Battery Primary lithium batteries are commonly used with tactical lights, due to the long shelf life, high specific energy, and gradual voltage decay over the battery's lifetime. Alkaline batteries also provide moderately long shelf life and low initial cost. In powerful lights with high current draw, the high internal resistance of alkaline cells results in decreased effective capacity. As the rate of discharge increases, a greater proportion of the cells' power is wasted in its internal resistance. Because of their low internal resistance, lithium batteries are often the primary cell of choice when a high rate of discharge relative to nominal capacity is required. Lithium cells will also provide better performance in cold weather than alkaline cells. High-quality lithium cells are less prone to leakage of electrolyte than alkalines. Rechargeable batteries, such as NiMH and Nicad, are economical options for lights with heavy usage. Rapid capacity loss in comparison to alkaline and lithium batteries limits the use of rechargeable cells to lights in frequent use. With a lithium-ion battery or a low self-discharge NiMH battery, rechargeable battery shelf life is extended. Several new models of tactical flashlights incorporate the ability to be recharged from a USB cable. Bulb Bulbs are chosen based on the desired light output and battery life. Generally, high performance bulbs are used, such as xenon bulbs or high power LED lights. LEDs provide maximum battery life due to their energy efficiency, and 2000s technology has greatly increased the light output of LEDs. At one time, xenon bulbs offered the brightest light levels, but recent high-power LEDs are brighter and more efficient than comparable xenon-filled incandescent lamps. Most importantly, LED bulbs are not subject to filament breakage due to the shot recoil of a firearm. Recent advances in high-lux, high-efficiency white LEDs have led to a wave of brighter and more energy-efficient tactical lights. Illumination types Tactical lights can be fitted with lenses to produce certain colors, Colored lights or filters provide flexibility for different purposes. Red lights are best for preserving night vision for the law enforcement officer, due to their minimal impact on the rod cells in the eye, while blue light provides high contrast for detecting blood. Light in the infrared spectrum is only visible through night vision devices, allowing the operator to see clearly while reducing the visibility to those not equipped with night vision equipment. Tactical lights are sometimes combined