I.R.
Lots of questions!
According to the theory of relativity, no matter what your particular frame of reference, you will always measure the velocity of light to be 'c', or approximately 300 million centimeters per second. How fast you're travelling doesn't make a difference in this context. From your viewpoint, shining the flashlight would look just like it would if you lighted it at *any* other speed.
As for light hitting your eyes, it isn't a matter of dissipation. The photons of light that hit your eyes are absorbed by the atoms in the light receptors in the retina, causing the electrons of the atoms in question to increase its energy level, which indirectly triggers an electrochemical reaction in the nerve connection to the retina. This electrochemical reaction travels down the optic nerve and triggers a response in the visual cortex of your brain.
The energy content of a photon is directly proportional to the frequency of the radiation, not its velocity. Red light has less energy (lower frequency) than blue light (higher frequency). Since photons have a proper mass of zero, they don't have momentum as such (although there is a recoil effect when the electron in an atom absorbs a photon, and an equivalent recoil when the electron releases a photon).
Simple answer, light photons are absorbed, not dissipated (the contained energy is applied to the system, but it is quite small overall, but it can be overdone, as evidenced by the fact that viewing the sun without protection will destroy your retina (energy overload)).
So if you can get a car to go at the speed of light and turned on your headlights, from your vantage point, it would look perfectly normal (actually, you can get close to the speed of light, but you can't actually reach that speed, as the energy required to accelerate you would be infinite, relativity again).
From the viewpoint of a distant observer, if you were moving away from him, and your headlights were aimed in the direction of your motion, he would see nothing, as the photons from your beams would be outside of the scope of his observable viewpoint. If your headlights were aimed at the observer, and you were travelling away from him at near the speed of light, the frequency of your light beams would be 'red-shifted' or lowered in frequency probably to the point where they would now be identified as radio waves in the very low frequency band.
If your headlights were aimed at the observer, and you were travelling toward the observer at near the speed of light, the frequency of your light would be 'blue-shifted' or raised in frequency, and would probably be identified by the observer as gamma radiation. You would also reach the observers location shortly after your light beams do.
If you were travelling at right angles to the observer, and were aiming your light at the observer, he would see it at the same frequency that was emitted.
The above is a very simplistic description of the events, doing the explanation justice would require a substantially longer post.
And if you think relativity is weird, you should try quantum physics
