LED headlamps on Impreza

[100SRV]

Hi,
a colleague tried replacing the H4 headlamp bulbs (filament) on his P1 with H4 LED. Only main beam functions. The pin arrangement for filament and LED is identical.

Any ideas why?

I have come across problems in the past with failure detection on LED turn lamps (and also side/tail on trucks) but this is a new one to me.

In the mean time I'll have a look for a schematic to see whether there are any wrinkles.

10SRV

[TheEnd]

I didn't now you can get LED headlights.
Depending on how smart the system is, it might be measuring the lower resistance of LEDs and assuming the bulb has blown, or than again, maybe the bulb is faulty.

[100SRV]

TheEnd said:

I didn't now you can get LED headlights.
Depending on how smart the system is, it might be measuring the lower resistance of LEDs and assuming the bulb has blown, or than again, maybe the bulb is faulty.

thank you for speedy response...
That is what I suspected...apparently no bulb failure indication but I will re-check.

[stevieturbo]

P1 has no such fancy features.

Manually power up the lamp to test if it actually works at all.

Although I'd say he has wasted his money anyway. Any reviews I came across about LED headlights all said the same thing. They're great unless you need to be able to see in the dark.

So they're useless as headlamps.

If they ever get Cree LED's for headlamps, they should be a possible replacement for halogens etc. But even SMD LED's are nowhere near a match for even a crap halogen

[tottacrolla]

Here is a link to some basic facts about LED lighting:

http://www.lazerlamps.com/technology/

and in particular:

"Efficiency
With LEDs currently achieving around 100 lumens/Watt compared to a halogen bulb of around 12-14 lumens/Watt"

[anonymous-user]

Led's fitted into conventional headlamp units designed for filament bulbs simply won't work,because the reflector design is all wrong, so it doesn't matter how many lumens of whatever the bulbs output.

Save you money.

[tottacrolla]

Max_Torque said:

Led's fitted into conventional headlamp units designed for filament bulbs simply won't work,because the reflector design is all wrong, so it doesn't matter how many lumens of whatever the bulbs output.

Save you money.

I believe it is the same with after market HID's ?
Certainly it is the case with my modified driving lamps.

[DrDeAtH]

TheEnd said:

I didn't now you can get LED headlights.
Depending on how smart the system is, it might be measuring the lower resistance of LEDs and assuming the bulb has blown, or than again, maybe the bulb is faulty.

LEDs have a high resistance
As does a blown bulb
This is why the problems persist.

A lamp filament has an inherently low resistance.

[Locknut]

I've never used H4 HIDs, but I believe they have only one light and they change from dim to full beam by moving the discharge tube slightly so as to change the focus. Is it possible that your friend's LED lights work the same way?