Retrofit LED bulds for brakes?

I fitted some in a car for a customer, but removed them immediately as I considered the brake light was not bright enough compared to a regular bulb.

They won't be legal unless 'E-marked', and still questionable if not original fit.

If you have a bulb failure system, it's likely it will show working LED's as failed, unless you fit a suitable value resistor in parallel with them.

Chris

I bought some LED replacements for the sidelights on the MX5 - they died within a couple of months.

If you get a decent set, they may be OK - but I've gone back to traditional filament bulbs.

Directionality.

Quite the reverse - usually not bright enough. Even with multiple LEDs.

A tungsten bulb has a smallish filament which the reflector translates into a broad spread of light at the appropriate brightness. Not easy to do the same with LEDs - which don't radiate light near 360 degrees.

A friend of mine had the same thoughts about a year or so ago and bought cheaply from Ebay. Most failed within 3 months with the most common failing being that they started flashing.

I've had no-name 12V festoon LED bulbs (number-plate and interior) fail within 12 months.

Unless originally fitted you may find that they are illegal - the "cover glass" lens arrangement is likely to be different for led clusters and filament bulbs.

A lot depends on the car, and whether it has CANBUS bulb failure detection. If it does you will need some heavy-duty resistors wired in parallel with the LEDS to simulate the load from filament bulbs.

Here are a couple of posts on another forum from someone who has fitted LEDs all round on his car:

I tried some on a horse trailer without much success when I was having problems which I suspected were related to voltage drop from old wiring, light units, plugs, and sockets.

They won't cure faults.

LEDs have to have a current limiter in the circuit. The crudest current limiter is a series resistor R ohms = (V supply - 0.6xleds) / current. That is only of use on power sources that are well regulated like computers and electronics. Cars have very unregulated supplies, can be anywhere between 15v down to 9V, can have some other nasty high voltage transients. So they require a voltage regulator or current limiter in the bulb assembly to feed the required stable voltage or limited current to the LEDs. The voltage will be less than the lowest car system voltage less the voltage drop in the regulator.

The supply to the regulator really needs a filter to take out any high voltage transients.

The voltage regulator can't increase the voltage, it can only reduce it. On a system that has voltage loss, that will reduce the current though LEDs reducing brightness.

Thanks all,

Guess that's a qualified "no" then. Big heavy sub woofer will have to shift out of it's space for bulb swaps.

Hmmm, what's the resonant frequency of a typical light bulb fillament? :-)

Time to buy better bulbs than Halfords cheapies...

When I ran a motorcycle shop I stocked heavy duty stop/tails, they have an extra support in the middle of each filament. Ideal for anything subject to a lot of vibration. Presumably they are still available.

But they draw *significantly* less current. Drop a couple of volts to a filament bulb and it goes quite dim. With (say) half the current you only drop one volt, and the LED regulator may well compensate completely.

A normal tungsten filament bulb is extremely voltage dependant too. I've not actually measured things, but my feeling is the percentage of light output varies more than it does with an LED fed via a simple resistor. And of course as soon as you go to an electronic driver for the LED, the voltage won't make any difference.

BTW, I don't think the car lights matter too much at 9v - the only time you'd see voltage that low was when the starter was operating - with a near flat battery.

LED drives for automotive LED drivers typically work over the 6 to 40V range. The LED is more likely driven with a AC voltage of greater than

200hz with the desired brightness being achieved with PWM (Pulse Width Modulation) techniques. Look closely at a car fitted with LED tail/brake lights and you should perceive a high speed flashing.

High speed? Like 200 times a second?

For the higher power bulbs (stop/reverse/indicator) I would say you are correct.

For 5W side/tail/number plate lights you can buy bulbs with the CANBUS resistors built in at the same or less than the price of the equivalent filament bulbs, and I reckon these are worth it. However, you do need to select the LEDs quite carefully for each application.

I've owned my Rover SD1 for about 25 years and sidelight, tail light and numberplate bulb failure is rare. To the point where I can't remember replacing any. Stop light failure, a different matter. One may need replacing every couple of years. But none fail regularly enough to make fitting a longer lived type a priority - especially if the performance is worse in any way. Such lights are a safety item, after all. Although on that car no bulb is difficult to change anyway. Not like some modern cars.

My Audi A8 requires the whole engine to be removed in order to change a headlight bulb!

I don't know what speed they actually use, but with some cars I do see a strobing effect as they cross my vision or I look away, but not while I am looking right at them. I see a trail of progressively dimmer red images (rather like using Windows with Mouse Trails turned on). I get the same effect when catching sight of the red man on Puffin crossings as I pass too. I've never understood why they don't use a higher frequency to prevent this.

SteveW