When two elements work together and the combined result is more than the sum of the individual element it is called Synergy. This is the principle around which the Extreme XPh Headlamp is build.
The end result is that you have a lighter and smaller light for the same constant apparent brightness with extended runtimes. Synergy is achieved by allowing the human eye to increase its sensitivity to light by slowly reducing the output of the light at such a rate that the apparent brightness remain constant. This is illustrated in the graph below: 
The benefits is that the Extreme XPh Headlamp is lighter and more comfortable with incredible endurance.
How does this work? 
There are two mechanisms in the eye which works together in accommodating variations in light intensity.
- The pupil changes size which allows more or less light in. This is quick but focus is effected due to depth of field changes. It is similar to the F-Stop on a camera.
- Retina sensitivity adjustment - This is a slow process and chemicals react to the amount of light present. Increasing or decreasing the light sensitivity of the retina. This is similar to the ISO setting on a camera.
The rate at which the Extreme XPh Headlamp changes its output was designed to allow the retina to change its sensitivity without affecting visual perception. In the eye retina a chemical called Rhodopsin regulates its light sensitivity. Rhodopsin is an extremely sensitive molecule. As long as the light is of low intensity, rods and cones quickly regenerate rhodopsin and the retina continues to respond to light stimuli. In high light intensity rhodopsin is bleached as quickly as rhodopsin can be produced making some of the rods nonfunctional. If this happens the cones take over. There is an automatic adjustment of retinal sensitivity to the amount of light present. This automatic adjustment is not only explained by the breakdown of photoreceptor pigments, other retinal neurons are involved. Here is a video explaining in depth how the eye works to change its sensitivity to light.
Light adaptation This occurs when we move from the dark into bright light. The bright light momentarily dazzles us and all we see is white light because the sensitivity of the receptors is set to dim light. Rods and cones are both stimulated and large amounts of the photopigment are broken down instantaneously, producing a flood of signals resulting in the glare. Adaption occurs in two ways:
- The sensitivity of the retina decreases dramatically.
- Retinal neurons undergo rapid adaptation inhibiting rod function and favouring the cone system.
Within about one minute the cones are sufficiently excited by the bright light to take over. Visual accuracy and colour vision continue to improve over the next ten minutes. During light adaptation retinal sensitivity is lost. You must have noticed this phenomenon. When you are outside on a sunny day, and then walk into a darkened room, at first you can hardly see anything. For example, if people come into a darkened movie theater they are constantly tripping and stumbling over their seats on the way in. However, after being in the theater for a while, you adjust to the lower light level of the theater, and it becomes very easy to see your way around. This phenomenon is called adaptation, and the particular direction I just mentioned, where you adjust from the light to the dark, is called dark adaptation.
Dark adaptation Dark adaptation is essentially the reverse of light adaptation. It occurs when going from a well lit area to a dark area. Initially blackness is seen because our cones cease functioning in low intensity light. Also, all the rod pigments have been bleached out due to the bright light and the rods are initially nonfunctional. Once in the dark, rhodopsin regenerates and the sensitivity of the retina increases over time (this can take approximately one hour to reach full adaptions). During this adaptation process reflexive changes occur in the pupil size. The Extreme XPh Headlamp works together with the human eye to smooth out the shortages of Dark adaptation. By maintaining a constant perceived brightness it extended its run time and allows you to function better. 
Source: www.chm.bris.ac.uk www.cns.nyu.edu