Brake Lights

[richdave]

I've followed a few BA XR6's on the road and they all appear to have a slight timing difference between the main lights on the car and the light in the spoiler...or at least that's what I see.

It seems the spoiler comes on earlier and off earlier. Is it just an illusion because of the LED's in the spoiler and standard globes in the lights? or due to relative size - the spoiler has a smaller area? Or is it actually due to the way in which the body control module activates them? :hiwelcome:

[Cashie]

the spoiler comes on earlier and off earlier

This is common with most cars with spoilers.

I have noticed it on many makes and models of cars.

It may be due to the fact the spoiler brake lights are normally LEDs and they light up faster than the incandescent brake lights.

[Cam]

Incandesent Bulb VS LED.

LEDs are a solid state device that produce light . LEDs produce light when electrons and holes reunite on the p and n sides of a pn semiconductor junction. (All semiconductors do this - LEDs are just designed to maximise the emmited radiation on a visible wavelength) This is by its nature a very fast process. I.e. Apply current and the light emmision start as soon as the first electron recombine with the first hole - very very very fast.

Incendesent light bulb rely on electrons 'boiling' off the surface of a piece of metal when it gets white hot into an atmosphere of special gasses. It takes time for the metal to reach the required temperature thus a small delay when the light is turned on. Also when the light is turned off the metal takes a finite time to cool below the temperate at which eletrons are able to escape into free space, thus a small delay turning off. A point in case would be high power high beams or spot lights on a car - we all know that take a second or so to turn on and a second or so to turn off.

I guess you think I'm rooting for this as the explanation for why they seem to come on slower. I doubt that that is actually the whole story.

The difference in turn on time is, I doubt, enough for it to be that obvoius to the human eye. It would probably be an exacerbating factor in what is probably an optical illusion.

So I guess after all that I havnt helped at all!!!!

[richdave]

Thanks Cam for the detailed explanation.....being in electronics myself all that theory sounds familiar in a distant (oh say 15 years ago) sort of way...

I suspect that it is really just an illusion though....

[Turbo6man]

It is no illusion richdave and Cam is exactly right - his theory is quite simply the reason why you notice the LEDs in the spoilers coming on earlier. If you check out a car with a normal globe in the spoiler you will see that all the brake lights come on together.

[Dagabond]

I tried my best but, i couldnt get to the back of the car fast enough after pressing the brake pedal to see if it's correct or not......

[saleen]

hehe

[Turbo6man]

Dagabond> you are a dag heheheh.

[Cam]

Here is some info from AutoSpeed.com.au...

High intensity LED brake lights have major advantages. When compared with incandescent lamps, their faster illumination time gives following cars significantly reduced stopping distances. Incandescent lamps used for automotive lighting have turn-on times in the range 100 - 300 milliseconds (ie up to one-third of a second). In comparison, a LED lamp has a turn-on time of 100 nano-seconds - pretty well instant!

Those turn-on figures assume that full battery voltage is available, but voltage drops are often present in brake lights. If subjected to reduced voltage at the lamp, turn-on times for incandescent lamps are even longer. With a voltage drop of 4 volts, the turn-on time of an incandescent automotive bulb can as much as double. The brightness of brake lights is also greatly reduced if the lamp is subjected to this lower than design-level voltage.

Studies have indicated that LED rear brake lights provide a braking response time advantage of between 170 and 200 milliseconds under favourable road conditions, and up to 300 milliseconds under adverse conditions. A 200 millisecond improvement in braking response is equivalent to a reduction in the stopping distance of 5.8 metres at a speed of 105 km/h.

In addition, practical testing has indicated that the response time of a person viewing a LED brake light is actually faster than would be expected, even taking into account the shorter LED switch-on time. It's thought that a lamp that reaches full brilliance very quickly is more likely to catch the eye of the following driver than one that reaches full brightness only slowly.