The most often used technique to reduce the pulsing headlight effect is to install a capacitor. These high-speed devices store up energy that's delivered in a fraction of a second, supplementing the slow nature of the typical automotive battery. Still, this isn't the perfect cure-it simply reduces the pulsing until it's no longer your biggest concern in life.
Over the years, I have fielded this type of question several times and have dealt with the answer in quite a bit of depth. Yet the question still comes up in my e-mail inbox. I'm going to propose a solution that I think will totally eliminate the problem of lights flickering or pulsing under any condition. This idea will work and, although I haven't actually tested it, I've seen enough similar analogies that I wouldn't hesitate on trying it on the first vehicle I run across. If you're ever near the New York/Ontario border and are sick of pulsing lights, I'd be willing to run some actual tests on your car. Let me know at dereklee@mobiledynamics.com.
Anyway, here is the solution as I envision it: install a capacitor on the lights instead of (or in addition to) the amps. We think of a capacitor as an audio component, but it isn't. We simply apply millions of electrical components to the audio environment. In this case, the mobile electronics industry approaches the pulsing light problem as an audio problem. It really never was an audio problem; rather it was a problem with compatibility between the stock electrical system and the demands of additional aftermarket electronics. In these pages, I've always discussed solutions to suppress the current gulping nature of car audio amps rather than trying to fix the result. This comes from my troubleshooting background, where we always try to fix the cause instead of masking it elsewhere. In this situation, it makes more sense to solve a problem that's only cosmetic, rather than the more complex solution of fixing the root cause.
If you have a decent-sized capacitor (probably 0.5-1 farad) connected to the lighting circuit of the vehicle, the lights would have a constant supply of current being reinforced by the capacitor when another vehicle subsystem consumes too much current. To make this work, you'd need a high-current diode or rectifier to ensure that the current from the capacitor always flows in the direction of the lights, but not backwards toward the battery, alternator and everything else.
The second thing you'd need is a relay that would disconnect the capacitor from the lighting circuit when the lights are off. If you just connect the capacitor, two things will happen-the lights will take a few seconds to fade off when you turn off the car, and there's a possibility that the lighting fuse would blow every time you turn on the lights. Since a capacitor acts like a short circuit for part of a second as it charges up, the fuse is likely to object. To combat this, a resistor can be installed on the primary side of the relay to allow the capacitor to stay charged up when the lights are off. Then when the light switch is turned on, the relay will engage, connecting the already topped-up capacitor to the lights. Just remember to start your car every couple of weeks to compensate for the capacitor leeching from the battery.
Even without validation, I'm sure this solution will stop your lights from pulsing and fixes the problem at the most efficient point rather than at the cause.