The name "Surefire" clearly indicates the professional vocation of the company that produces the U2 Ultra. Actually, all the products of this USA constructor, are well-tought-out in order to resist in the time, in adverse conditions. How many times you had an unsuitable flashlight after a banal fall or a rainstorm, or the electrical contacts corroded from the battery acid or the saltness. With Surefire, these things simply do not happen.
The material which this "instrument of lighting" is forged with is a particular aluminum alloy, the same one used in the construction of the airplanes and of the space vehicles. Lightweight, it resists to the abrasions and to violent hits. The anticorrosion treatment of military type (anodization of type III) is unattackable from the most aggressive atmospheric agents. The mobile parts are protected with o-ring gaskets in order to assure watertight, also in case of immersion. On the whole, the structure of the U2 Ultra, can be launched against a rock,  crushed from a heavy vehicle, falls in water, without breaking itself.

The use of the LED as a light source, guarantees a duration of many years and a greater resistance to hits. The LED light has numerous interesting characteristics, as it can be read on the article "LED flashlights to the maximum power"
Lithium batteries supply a remarkable reserve of energy and work well in severe cold and warm conditions. If not used, they keep their charge for 10 years. In practice the couple LED/Lithium guarantees a flashlight always ready to use.

The dimensions are very compact, compared to the amount of produced light (Length 15 cm, maximum Width 3,5 cm)

The Surefire U2 Ultra grasps well, thanks to the knurlings on its body. Also with sweaty or grasy  hands, does not risk to slip off. The belt clip in stainless steel, allows a sure hook and resists well to traction and tears, in every condition of use. The switch button is protected by an antislide rubber covering. The on-off actions are signalled with a pleasant feedback under the finger. Also the metal ring for power control is equipped of knurled guides  for a sure drive.
The rabbets on the head of the flashlight, are good to avoid rolling. Is clearly visible the warning to avoid touching the lighting head, that become hot during prolonged use.
To avoid forgetting the light on, when is on a table, small rabbets are present on the edge of the flashlight. The light beams spiling off alert the user that the light is working.

Like a military instrument, this flashlight is constituted of three pieces: the head, the central body, the tail. These pieces are screwed toghether with anticorrosion threads and insulated with o-ring gaskets water resistant.
In the head is located the lighting system and the control ring of the luminous power. The LED used is the Luxeon V (5 Watt of power), set like a precious stone in the reflector planned with the computer.
The body hollow, accommodates the two lithium batteries and mounts the belt clip of generous dimensions.
The tail part contains the power switch constructed with stainless materials and resistant to the wear.

In order to vary the amount of emitted light, it is used an electronic circuit that regulate the energy amount. The six levels of brightness maintain a constant  intensity also when the battery begins to discharge itself. The control of the issued power is entrusted to an electronic circuit that increases the life of the batteries. To the minimal intensity, 40 hours of autonomy are caught up. To the maximum power, the level of brightness comes maintained for an hour.
In order to concentrate the power of the 5 watt LED and to create a ligh beam without shadows, a bezel of generous dimensions is used, with rough surface. The escape lens of the luminous bundle measure 3 cm and is protected from a glass in Pyrex, with optimal characteristics.
 

The shape and the structure of the reflector, guarantee a total absence of dark spots, often present in many professional flashlights. The type of projected beam is composed from a central zone of high brightness and from a uniform crown that degrades smoothly to the periphery. This spot-flood characteristic is very useful to to orient ourselves in total darkness. It illuminates the surrounding zone and at the same time far particulars can be seen. In the figure we can see a false colour diagram of the different light levels and the distribution of the light beam.

The six levels of luminous intensity, allow a remarkable versatility of use. The minimal level is suitable to read a map or find the bunch of keys fallen on the ground. The gradually superior levels, reach high distancies up to illuminate to day objects of small dimensions. To the maximum intensity is possible to take films or photos thanks to the color temperature near to the solar light. In the figure we can see the six levels of light comparison. Blue coloring is emphasized by the automatic exposure meter of the camera: in the reality the blue shading is present to the lower powers but tend to disappear totally to the maximum intensity.

A pocket lighting tool for those who doesn't want to risk to remain in the dark, anywhere. The U2 Ultra is good for extreme sport lovers, those people living in contact with the nature, the professionals of the civil protection,  the pilots, but also more skilled City-drivers. The lifetime warranty offered on the product, confirms the seriousness and attention dedicated in crafting and developing these flashlights.
I thank Surefire company that sent the test sample from California, giving me the emotion to use a "state-of-the-art" flashlight !

Homepage of the builder: http://www.surefire.com