Centre, high-mount brake lights are a good thing. The idea is that the light can be seen through the front and rear glass of the cars in front - letting you see a car slowing down well ahead of you in the line of traffic - and the placement of the light nearer eye level causes you to see it much faster. Some centre mounts use LEDs which have two advantages - they're quicker to reach full brightness than filament bulbs, and they stay brighter even if there are voltage drops in the wiring leading to them.
The result of the technology? You're much less likely to be rammed up the tail when you stop suddenly.
But what if your car has got a high-mount brake light powered only by old-fashioned filament bulbs? Wouldn't you like to get the advantages of LEDs? Sure you can - but previously there's been a major problem. Filament lamp designs have been constructed to use one or two bulbs which are huge when compared with LEDs. Put a typical 5mm LED (together with its dropping resistor of course) in place of the bulb and you're likely to get so little light output that it's pointless.
What's needed are red LEDs that are large and of very high intensity.
Trouble is, while these LEDs are available, they can cost anything up to AUS$13 each! However, we've managed to source a small number of high quality Sharp LEDs. Punching out an astonishing 18500 mcd (a typical 10mm red LED puts out 5-15 mcd....) they're so bright that it's impossible to look right into their beam without seeing red spots for some time afterwards! These LEDs are even designed for outside use, so are UV and high temperature resistant. We have them available at the AutoSpeed Shop for AUS$5 each (or 12 for AUS$50) until the stocks are gone. These prices include the 1-watt dropping resistors that need to be used with each LED.
So how do you turn your filament lamp dull-and-boring centre mount brakelight into a high performance LED one? We did the whole conversion on a two-bulb Lexus LS400 rear high-mount.
Out of the car, this is what the Lexus centre mount brake light looks like. Truth to be told, we weren't quite sure what we'd find inside - never having looked at the guts to find out!
It wasn't good news - just two filament bulbs with some big reflectors. Pretty low-tech, and not nearly as effective as we could make it. Making it even worse was that these bulbs were beginning to blacken.
The reflector assembly pulled straight out, and then we were left with the bare casing, that included the red lens. You might not be as lucky as this - your car's design might not leave anywhere near as much room. Fit and fiddle to give the best results.
Here's the new-tech upgrade - or one of them, anyway. It's a 10mm ultra high intensity Sharp LED, punching out 18500mcd and yet with a consumption of only 50ma. Put in nine or ten of them and the folk behind will sure see you stopping!
And here's the component that you need to run in series with each LED if you're not to fry it - a 1-watt, 220 ohm resistor. The resistor limits the current passing through the LED - vital if it's to last more than a second or two.
What's needed next is a nice piece of pliable but strong plastic in which to mount the LEDs. This started out as an 'unbreakable' school ruler and was perfect. With a file and some fine sandpaper it was smoothed and shaped 'til...
... it fitted perfectly into the brake light moulding. It was even easy to bend it a little to match the shape of the lens, so that each of the LEDs would look the same brightness and size when viewed from behind.
After it was shaped the next step was to mark out and drill the 10mm holes. We ended up with nine of them. Why not ten? Well, there's no magic in the number 10 and using nine gave a good spacing.
If you drill the 10mm holes without wriggling the drill bit around too much, the LEDs will be a good tight push-fit into the holes. If you go oversize, some silicone sealant can be used to hold them in place.
Mounted in the brake light with some dobs of silicone sealant and with the individual resistors all in place, this is what it looks like. This top view is a bit deceptive - check the circuit diagram below to see how those resistors are wired.
The LEDs are polarity conscious - they need to all go into the circuit so that their long leads are connected to the positive supply. The resistors will get warm to touch - maybe even hot if the brakes are on for a long time - so they shouldn't be in contact with anything.
One big-arse car with a VERY bright centre-mount LED brakelight. And if you don't reckon it's too bright, check the brightness of the other brakelights... cameras can be a bit deceptive. Rest assured, you won't be disappointed!
The AutoSpeed shop has obtained a limited quantity of Sharp Japanese-made GLOZJO42BOS ultra high intensity red 10mm LEDs. Click here to go to them.
The Tech Advantages
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.