In traditional halogen H4 bulbs the low beam filament (the one with the reflector/shield) point in a 180 degree field and the high beam has no shield and has a full 360 degree coverage. This is how all H4 light assemblies are designed to use.

Why then are there no H4 LED bulbs which use this layout? They all have terrible design or are only designed for low beams.

Actually that's not being fair, Phillips have a product that does this, but they are quite pricey. 400AUD pricey.

  • 1
    Are you talking about cheap chinese bulbs? In that case the answer would be just that - they're intended to be cheap to attract buyers, not correct. Philips did it correctly and it didn't come out cheap. Apr 18, 2016 at 12:34
  • Ones like this (img.dxcdn.com/productimages/sku_51110_1.jpg) are absolute rubbish, however ones like this (i.ebayimg.com/00/s/ODAwWDgwMA==/z/-2AAAOSwZVhWSr~Q/…) at least have a the low-beams designed properly. Why don't they just have a ring of LEDs just below the main chip to constitute the high beam I just don't know
    – Tanenthor
    Apr 18, 2016 at 12:40
  • Also consider that there's no such thing as a 360 degree LED. Modern surface mound LEDs have a 60-45 degree range and require reflectors or lenses to spread the light out more if needed. Multiple LEDs can be used for a wide angle, but that increases cost and complexity.
    – JPhi1618
    Apr 18, 2016 at 14:38

2 Answers 2


I think you hit it. Cost, most of the LED headlights are made to just pack as many LED as possible into the H4 package as possible, but a small percentage of them are actually designed to mimic the H4 fillament. Most of the cheap LED bulbs aren't DOT certified, so look for the certified ones, they give you better performance. I'd recommend a brand, but you're already aware of the Phillips.

  • 1
    Also, it would seem to me, if you have a bunch of LEDs packed all around the bulb area and you have two separate power sources (high/low), the part the LEDs are located in becomes its own shield. Low just turns on the bottom half (or whatever half) while the high beam side would turn on all. I don't know if this is the way it works, but it sounds reasonable. Apr 18, 2016 at 14:04
  • TBH I'm quite surprised any H4 LED bulbs are DOT certified, but then I've yet to see any LED headlamps that don't either suck or cost a billion dollars or both.
    – John U
    Apr 18, 2016 at 15:30
  • I have a very nice set of H13 LED bulbs in my Jeep that are certified, but they cost about $100 for the pair. Apr 19, 2016 at 1:56

The biggest issue with high-intensity LED's is heat dissipation. Heat is an LED's #1 enemy, regardless of the LED package.

High-powered LED's that put out about 2 to 5 watts of light each (9 times more than the power they consume) need be be epoxied to an aluminum or copper heat sink, maybe even fan cooled.

But I see many LED street-lights with LED's burned out, probably due to a poor heat-sink procedures. They did not even last the 5 years expected of them.

High intensity lights for cars have the problem of no space to dissipate the heat. I do not think they will compete with quartz-halogen lights until the reflector itself is an array of LED's epoxied to a metal plate. LED's for brake and turn signals will become more common as they can be mounted flat on a metal plate to absorb the heat.

They have already done this with some high-intensity flashlights, getting the basic engineering right first. LED's can last for 20 to 200 years continuously, if you can keep them cool and not run them at full power.

( Based on 100,000 hour MTBF at nominal drive current and temp ambient of 25deg Celsius )

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