<VV> LED Headlamps WARNING, GEEK ALERT!!

[jvhroberts at aol.com]

First of all, they are NOT xenon headlamps, they are metal halide HID lamps. And the efficiency is, in fact, documented. Forget the handwaving and look at the numbers. 3200 lumens for 35 watts for HID (about 92 lumens per watt), as compared to 1000 lumens for 55 watts with halogens (less than 20 lumens per watt). As of today, LEDs can do MAYBE 25 lumens per watt at the kind of power levels used for headlamps. These are system efficiencies, not just the lamps. And yes, LEDs DO require 'active' electronics. They need a ballast to efficiently regulate current. HIDs have replaceable bulbs. And as of now, for the same lumens, LEDs don't use any less power than halogens. But there is the Gee Whiz thing!

As far as KISS, well, today's cars are more complex than ever, yet they are more reliable and durable than ever. 200K without any major maintenance is routine, whereas in the 60s, 100K without major maintenance was more the exception. 

I suggest?abandoning the hand waving, and explore the links I sent earlier. 


-----Original Message-----
From: tony.underwood at cox.net
To: virtualvairs at corvair.org
Sent: Tue, 13 May 2008 3:20 pm
Subject: Re: <VV> LED Headlamps




---- jvhroberts at aol.com wrote: 
> HID is still more efficient, by a BUNCH!

  I'd still take that bet, IF you consider the somewhat complicated electronics 
required to fire the xenon lamps, along with the rest of the stuff necessary to 
dim them  via pulse width etc.   That circuitry uses up power as well, although 
admittedly the xenon tubes do put out a lot of light for the power inputted to 
them (not counting the energy used up in the inverter necessary to fire them).  

It's a complicated system that still in the end fires a xenon lamp that has a 
finite lifespan and when they fail they're not all that cheap or easy to 
replace.    

It's not that HID lamps don't work; it's that they're complex and technically 
cluttered with lots of extra "stuff" to do the work that other lamps have done 
for decades.    The KISS principle is unknown amongst automotive engineers these 
days, one of the reasons cars keep costing more and more.   

...and again, with LED tech advancing every day, it's not going to be long 
before the Very Simple (relatively speaking) LED lamps could well overtake 
anything else out there currently, with not only an efficient power conversion 
factor in their favor, but a very long working life as well.   
 


>  It puts out about 90 lumens per watt, whereas power LEDs suitable for 
headlights are doing about 25 lumens per watt, 

There are LEDs available now that approach 40, and more improvement is on the 
way.  LED lighting is gonna be the way of the future simply because they're 
simple.   No active electronics needed, and no high currents or heat to deal 
with.    


> which is about what a low voltage halogen does. Agreed, the electronics are 
pretty sophisticated for HID, but they are efficient.   

...and if they fail for whatever reason, how expensive will they be to repair?   
The car could be deadlined for days just to fix the headlights.    With that LED 
light, it's as simple as a bulb replacement from Auto Zone, and as time passes 
you *will* see LED light replacements there...  but I betcha dollars to donuts 
you won't be seeing HID replacements for average cars that will plug in like the 
incandescents they replaced.   

Oh, I'm sure the HID kits will be out there if you wanna spend the better part 
of a thousand bucks to convert.   ;)   

> LEDs, to be efficient, also require a PWM current regulator

...a circuit board the size of a playing card could contain everything needed to 
do this, and cost very little once mass produced.   it could offer up 
continuously variable illumination not unlike HID.   

> so as not to burn away power through a wasteful current limiting resistor. 

Then again, it's not as if we don't have current to burn with the car's standard 
electrical system, and even then the power requirements would still be less than 
what Halogens would draw.     

> Cooler? Not yet, maybe never.   

  It wasn't that long ago that nobody had a clue about making a white light LED 
in the first place...  now they're available as replacements for house lighting 
and spotlights to light up your patio in the back yard.    It's not gonna be 
that much longer before we start seeing them available as replacements for just 
about any incandescent light bulb.    Tech is relentless; current issues will be 
weeded out and cooler brighter more efficient LEDs will be coming soon.   

> HID and halogen operate at such high temperatures that most of the heat they 
generate is radiated out with the light.   

Not in the case of the HID stuff... with its accompanying electronics which 
while quite efficient still do consume power to do what they do.   Even an 80% 
efficiency factor (typical of most of those types of inverters) is still 
radiating 20% of the power it uses as waste heat.   And xenon tubes DO get hot, 
enough to sear you if they're driven hard.  

They're nifty items right now, but time will condemn them as too complicated and 
ultimately too expensive for mainstream use.  

...anybody remember capacitive discharge ignition systems?   

> Longevity isn't much of an issue with HID, as the projected life span is 
several times that of halogens, and for most users, will outlast the car. 

...IF the tubes aren't driven too hard, like running full brite for any extended 
length of time.   Xenon tubes have a finite lifespan, based on usage, not age.  

I used to work in a field that had xenon tubes in its arena and I've replace a 
few in my times.    I've seen them simply wear out in a year or so depending on 
use, and I've seen them driven hard enough to melt the lenses covering them, and 
I've seen them experience capacitor explosions in the inverters that showered 
the insides of the inverter case with tin shrapnel... typical electronics issues 
the likes of what tend to happen on occasion to just about any electronic 
devices.   Such things DO happen...  just because they're kewl doesn't mean 
there's not gonna be random HID laighting failures and they *will* be expensive 
to fix.    

> And due to the high cost of LEDs, they are rather overdriven to keep the 
installation costs down. Shame, because mos
>  t power LEDs are most efficient at around half of max rated power. 

...which is gonna continue to improve as time passes.   


> Cost? Well, LEDs are DAMN expensive on a $ per lumen basis. HID is next, and 
halogens are dirt cheap! LEDs are getting cheaper, but the lower floor is 
limited to a rather high level due to the more complex construction compared to 
either HID or halogens. HID bulbs are actually VERY simple! 

Yep.    They're VERY simple, being nothing but a xenon gas filled glass envelope 
with two electrodes embedded in it and a firing electrode wired to the tube 
somewhere, but that's where the simplicity ends.  The electronics they require 
are hardly simple, and involve some considerable complexity to exploit xenon 
tube technology to its best.   


I'm not down on HID lighting from a performance standpoint; I'm critical of its 
expense, costing much more than other comparable lighting.    I for one will 
patiently await advanced LED lighting, which IS on the way and will begin to 
replace incandescents sooner than a lot oif people might realize... particularly 
those so-called "lamps of the future" mercury filled florescent lights that 
everybody seems to think are so cool and the answer to "global warming".  

Still, I'm not concerned about house lighting... that will come soon enough.   I 
wanna see retrofitted LED lamps for older cars, replacing the headlights in 
something from the '60s, like a Corvair.      

If nothing else, it would help reduce cooking  of those dimmer switches.   

tony..

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