Timm's BMW E31 - LED Headlights and Fog Lights
 

I have LED Sidelights now - they are exceptionally bright and white, the only problem being that the main beams, fog lights and dipped-beams are the standard Halogen. They are certainly bright enough, but look slightly yellow

There are a huge number of LED headlight bulbs available in 2015 - although the H1 bulbs are fewer in number because of the small format. The main problems with LED H1 replacements are:

• The bulbs are huge because they need to be cooled with an external fan or a massive heat-sink of some type, usually both. Have you heard that LED's are a cold light source? Well, they don't radiate heat like a tungsten filament and that's the problem - the heat has to be conducted away from the LED to an external heat-sink.
  
  If the bulb you are looking at doesn't have an external heatsink (something stuck on the back of the bulb), then don't even waste your time trying it - it will not be anywhere near bright enough. Even the most efficient LED's will be dissipating 10W of heat - and without a heatsink it would soon melt and is a good clue that the light output is feeble. There are loads of this type around, none of them are any good.
   

• The bulbs are heavy - and the H1 fitment relies on a little metal clip to secure the bulb in place which is fine for the H1 Halogen but not strong enough to support a great lump of a bulb.
   

• The LED bulb usually needs an external voltage-to-current converter - that needs a home somewhere
   

• The lighting source (the LED's themselves) cannot mimic the omni-directional filament light source

Still, I'm willing to give it a go just for fun - on the E31 the only place it is going to fit is in the pop-up main beams - and only just. Here's what the bulbs look like:

Let's face it, it's a whopper, it's going to be tricky fitting that anywhere - but we haven't finished yet, there's the power supply to find a home for:

Here is the removable H1 collar which is held in place with a sprung ball:

The bulb demands around 1.5A at 12V - which is 18W or so - and at 100 Lumens per Watt the output could be expected to be around 1800 Lumens - a little brighter than a 55W Halogen such as the Osram Nightbreaker.

I spent an hour or so trying to fit the LED bulb to the main beam position, it's blooming awkward to say the least. The 'H1' collar can be removed from the LED stem so it can be fitted to the headlight first - that seems like a good plan until you realise that there is no room behind to fit the bulb itself.

The only way to do it was to keep the collar fitted, but loose on the stem, get the clip over the collar and then push the bulb forward. The collar is held in place with a protruding sprung-mounted ball on the stem that locates with a hole in the collar. Well, it's in there, but I would have thought a bumpy road would soon see it popping back out again.

For the tests I've covered all of the lights with cloths so that only the upper main beams will throw any light:

Looking at the front of the car, the LED bulb is on the right, the standard Halogen is on the left. On UK models the lower FTP main beams come on at the same time as the upper ones so they are covered as well. First impressions are - well, it's certainly white - and it looks bright!

But, what about the beam pattern, that's not so good:

The light is going everywhere! If the beam pattern was the same as the Halogen then the LED would be a winner as far as the brightness was concerned - unfortunately the light is going in all directions. By introducing shadows in the picture we can tell the relative brightness of the beam as shown below:

As can be seen, the light that does go the right way is not so bright as the Halogen (Osram Nightbreaker Unlimited) and the central beam patter is poorly defined. It's a shame, I really fancied LED headlights - but the manufacturers are not there yet. Just the same as the Xenon retrofits, unless the reflector is designed for the bulb being used, it just isn't going to work.

A look at the lights from the front shows one of the problems - the beam pattern has a bit missing:

So, it's back to the Halogens, they might be slightly yellow compared to the LED sidelights, but with all eight Halogens on at the same time, there's certainly enough light:

I'll try again if the manufacturers come up with something new - there are quite a few with smaller LED sources on both sides of the stalk, but they still have a fan fitted to the back with no chance of fitting them anywhere except the main beams. There is also a model with a passive heatsink made from layers of braided metal belt - that at least has more of a chance of fitting in the headlight assemblies. But, even that manufacturer has to state:

"LED bulbs do not disperse light into a lens designed for a halogen light the same way a conventional bulb does, no matter how bright the LED may be. For this reason performance varies from lens to lens"

These bulbs are becoming quite popular in the UK - and they are quite obvious when fitted to a car heading towards you - the lights are reasonably bright and white, but they cause so much dazzle due to the poor beam pattern. They can't be providing a safe amount of light in the right places but this doesn't seem to stop them being used.

 

A bit about Wattages, Brightness and Lumens

Let's start with some useful information:

• A decent H1 Halogen bulb (such as the Osram Nightbreakers) produce around 1500 Lumens of light
   

•  For every Watt of power the Halogen produces around 27 Lumens of light
   

•  A Halogen bulb converts only 3% of energy into light - the rest is turned into heat
   

• The light spectrum produced by a Halogen bulb is perfectly suited to the human eye
   

• The most efficient LED's can produce 150 Lumens per Watt - around 5 times as much as a Halogen
   

• The most efficient LED sources are still only 20% efficient - 80% of the energy is converted to heat
   

• The light spectrum produced by LED's is not continuous - it has gaps at various spectral frequencies
   

Given the above information it would seem quite easy to manufacture an LED bulb that would be just as bright as a decent Halogen - you only need 10W of electrical power to produce 1500 Lumens of light if the latest LED sources are used. The problem with LED's though is that they do not radiate heat - which is what Halogens do. Instead of the heat being radiated out of the headlight (you can feel the heat being radiated just by putting your hand in front of Halogen headlight) - the LED's must have the heat dissipated from the metal slug of the device.

The second problem with LED's is that they are not a resistive load, you can't just bung 12V or so into an LED device like you can with a tungsten bulb and hope it will light up. Instead, they require a fixed current source - that is why you get a little metal box with the LED bulbs. The box will usually contain a switched-mode power supply that produces a current-limited voltage to the LED's.

Don't believe that claims of LED bulb sellers - most of it is made up. A common ruse is to say that they are using 50W LED's from Cree (or other manufacturers) - they may be using 50W LED's but there is no chance they are putting 50W into each LED within the assembly. To check their claims, run the LED bulb from a bench power supply - the ones I have tested demand approximately 1 Amp at 12V (12W) - and one demanded 1500mA which is 18W or so - even when they are claiming 50W

The Lumens output claimed by sellers also follow the same ruse, they often quote the luminance of the device at the peak current it can withstand - but fail to explain that they actually run the LED at a fraction of the maximum current.

Time for a cup of tea