Take a look at Figure 1 – this is an oscilloscope trace of the response of the old incandescent amber lamps. The data was acquired last year at the drag strip in Pomona California. Pictures of the testing process can be viewed at www.RaceTec.cc/test_photos.htm. Notice how the old lamp’s brightness increases slowly over a period of time. In fact the lamp does not reach full brightness until 0.160 seconds after the tree is activated! The ripple in the brightness response is an artifact of the 60 cycles per second alternating current that powers the lamp. This is a typical turn on characteristic of all incandescent lamps. The slow turn on is because the lamp’s filament has to heat up before it begins to glow – and that takes time.

With the old lamps the question was – when does the driver see the amber lamps? Depending on conditions, such as the sun’s brightness and position, the driver would see the lamp any where from 0.005 seconds (during twilight racing) to 0.025 seconds (with bright sun on the tree) after the tree was activated.

Overlayed on the graph in figure 1 is the response of the new LED amber lamps. The LED lamps go to full brightness within micro seconds (millionths of a second) after the tree is activated. You see the amber lights immediately upon activation which can be up to 0.025 seconds earlier then you were able to see the old lamps.

By the way – do you know that the amber lights are not directly activated by the starter’s switch? At most tracks there is a computer generated random delay between the moment the starter toggles his switch and the tree is activated. The purpose of the random delay is to foil your attempts to learn the starter’s rhythm and jump on the tree.

Back to the point - So how do you compensate for the LED lamps? If you are running a delay box it is prudent to add at least 0.015 seconds to the delay the first time you encounter these lights. Adjust the delay from there as you gain experience with the LED lamps.

Then what? You were probably adjusting your delay box throughout the day to adapt to changing conditions, e.g., increasing the delay to compensate for the fact that you would see the tree faster as the sun fades. With LED lamps that is no longer necessary. You’ll only have to adjust your delay to compensate for your consumption of cheeseburgers or Red Bull.

What if you’re not using a delay box? If you are cutting close lights without a delay box you’ll have to take steps to add some delay to your launch. This can be done by putting a little slop in your launch button or whatever mechanical linkage you launch with. There are many brands of launch buttons, and some have longer button travel than others. With the old lamps these long travel buttons were avoided – but now they may be useful. These buttons can add delay to your launch.

Check with your track officials to see if and when they’ll be using LED lamps. If they are still using incandescent lamps then be sure to check with the tech crew each race because they are sure to be there soon.

For that weekend at least you’ll have an advantage over the less informed competition.

Author: Tim Duffy, Design Engineer for RaceTec division of Velotec, www.Racetec.cc or (714) 695-1500 for more information