When I flew to the UK last month and went through British Customs, they briefly had me stand and face a camera so they could take a picture. I didn't occur to me until you mentioned it here that this would likely be for their facial recognition system.

Your home so I guess your mug is not wanted <img src="/forums/images/graemlins/kewl.gif" alt="" />

otherwise it's grab the ankles time <img src="/forums/images/graemlins/zombie.gif" alt="" />

I'm pretty familiar. I'll give you a rundown later if I remember.

Brian894X4, here's a quick rundown on laser and radar theory.

First of all, they all operate on the Doppler principal. Doppler doesn't neccesarily have to be sound, but that's the clearest example. Think of a train approaching a crossing, sounding it's horn. The pitch of the horn is higher as it approaches than if it were sitting still sounding the same horn. This pitch increase is variable, based on the approach speed of the train, the faster the train is moving, the higher the pitch. This is due to wave compression. The same goes for the train passing by. As it approaches, the pitch is high, as it departs, the pitch (from your perspective) is lowered. This is caused by the streching of the sound waves.

If you think of what the horns actually are, it helps make the correlation to laser/radar. The horn is really just a membrane beating on the air and sending the pulsed vibration down a tube and out of a flared end. Laser/radar works in the same manner. A measured pulse is sent out through the radiator or lens of the laser/radar device, and it's the pulse compression/stretching of the returned signal that the radar/laser device is using to interpret the speed of the target (really, target is used loosely here, since radar/laser devices only show the strongest returned signal). Make sense so far?

Here's the really fun part.

Since laser speed detection equipment can only interpret the strongest signal it receives, if you can shine a really bright light (in the same frequency range as the device) at it, you will dilute the returned signal to the point that it causes a severe delay in the signal aquisition of the receiver. In short, make it so the suspect vehicle gets a lot more time to slow down before the speed is displayed on the device.

Think about the lights on the front of your truck. If you turn them on and put your hand in front, your hand gets warm. That's mostly due to particle (photon) collision against your skin in the infra-red color temperature range. Since vehicle lights use extreme heat to produce light, you'll get a lot of radiation in the infra-red end of the light spectrum. Laser speed detection devices also use infra-red light, but it's a much more directed signal at a lower energy level. After it's diffused (by, say, the license plate) the returned signal, while strong, is still easily diluted with broad-spectrum lights, to the point that it either doesn't have enough data to interpret, or too much.

Since most places don't let you drive around with big, bright lights on, people put a filter over their lights so they won't be seen. That's in infra-red pass filter fasteddy was talking about. It only allows the disruptive light pass through but retains the rest of the spectrum, by converting the light into heat (and thereby contributing (though in small part) to the disruption).

Clear as mud?

You have traffic lights. <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/scared.gif" alt="" />

This county is so poor we don't even have stop or yield signs at all corners. Stop lights are out of the question.

The State Gestapo around here had to practice aiming and firing the laser scoped speed guns to "qualify", just like with the sidearm. Used an old license plate as the target. I took the hint and removed all the shinies from the front that I could. Even the "BAMA" tag. Bear would have understood...

Brian, I hear really talented cops could whistle into the radio mike and make the radar speed gun read what they wanted it to. Something about "calibrate" mode stuff...

paint your truck in IR absorbing paint. Milsurplus helicopter paint would do nicely..

Enlist a "rabbit" who you entice to run faster than you by pissing him off so every time you speed up, he does, too, and you fall in behind with the cop bait out front and obvious. Young ricers work well for this for higher speeds. Old yankee farts do better at intermediate speeds. Look for a shiny red old yankee fart. The high blood pressure makes it work better, as does a wife who waves her hands while she harangues him from the admiral's seat...

Don't go faster than the fastest trucks. This can easily yield an 80mph cruise, and is entertaining if you like near misses and truck lane weave from the fast big'un.

Yellow light time used to be state mandated at 4sec. Shortened to three a few years ago. Stated purpose: speed traffic flow. Real purpose: revenue gen.