The brightness depends on which color LED you get. They have different beam angles, and different brightness. Regarding the Photon I and the ASP, their main drawback is the fact that they have only momentary on switches that you have to keep pressing. If you are concerned about preserving your night vision, then green is the best color to get. Your rods, which are responsible for night vision, are very receptive to green light. This means you can use a lot less light to see what you need (this is why the military is switching to green lights from red ones). It is the brightness of the light that ruins night vision, not the color. Since your eyes perceive objects better under green light, you can use dimmer light. This makes the Photon III your best option, because you can set it to a dim, medium, or bright mode as the constant on setting. You can always press the momentary switch for immediate brightest setting. I have a white Photon II, and a green Photon III. I love the III.
Mike