Are your headlight lenses getting cloudy?

The key thing to realize about "efficiency" is that it is, by
definition, a unitless value. Lumens/watt isn't efficiency,
because it isn't unitless.

In common use, sure. It's sloppy, though.

 

As a space heater, a light bulb is 100% efficient.

As a light source, it isn't. Efficiency would be watts of usable
light output per watt of electricity input.

 

In addition to the lenses, reflector efficiency is very low in these molded
headlamp units. My Explorer has some of the worst lighting I've ever driven
with. Bad enough on a good night, dangerous on a rainy night.
The need to engineer highly efficient reflectors and change the lens formula
so that it remains clear. Or maybe go back to glass with evaporative
deposited aluminum reflectors on aircraft aluminum housings.
If ever there was a good reason for a recall, this would be it.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

 

nasty


My wife's '89 Mitsu Galant has no yellowing or cloudy lenses at all. Why?
Because they use GLASS lenses. Nothing substitutes for glass when it come to
longevity.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

 

Slight slip. 1993 Dodge Colt. Piece of crap from the day it was built,
headlights so yellow in 2002 that they looked like fog lights.

 

My 2001 Merc plastic lenses (not US, mind). That's more than two years old,
I think.

Even with Xenons fitted.

I understand that my version of model range has had plastic lenses since
launch in about 1998. Related cars have probably had plastic lenses for
some some years, too.

I hope it helps.

DAS

For direct contact replace nospam with schmetterling

 

If light itself is not heat, then no. A certain portion of the energy
in gets converted to light, the rest is heat. They have to add up tho
the input energy. So if light is not heat, then a light bulb is no 100%
efficient.

Is light considered heat? I'm not an expert in this field, but I think
heat is in only the longer wavelengths (including infra-red) of the
elecromagnetic spectrum - visible light is shorter wavelenghts - and UV
is even shorter - neither heat nor visible light). So no - I don't
believe your statement about the light bulb being a pefect heater is
correct.

Isn't that what I was saying? Lumens and watts are both units of energy
- certainly there is a conversion factor between lumens and watts.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Unless a rock of just the right size hits it - you might get a tiny nick
in the plastic, the glass will break requiring replacement. 8^) I'm
guessing that glass would hold up slightly better against sand blasting,
but not sure about that.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

How do the H1/H2/H3 bulbs produce so much more light than an H4 for a
given wattage? Better technology, or do they trade output for bulb life?

 

You're right; my definition is clumsy. All I was pointing out was that
all the input energy was coming out.

Floyd

 

Actually, all the light - both visible and infra-red - produced by a
lightbulb (of any kind) are eventually converted to heat. They
are eventually absorbed by some surface and converted to heat.

Floyd

 

Bill, arguing that you're right and the rest of the world is wrong is
generally a fruitless exercise. Trust me on this one; I know! ;-)

 

H'm. I'm interested to know how you arrive at that conclusion.

I'm guessing it's a pre-2003 model. The '03 up Explorers actually have
rather efficient and well-focused low beams, but the previous models have
three generations of really awful headlamps.

I'm still curious how you arrive at the idea that the reflectors in your
lamps aren't efficient. Generally, reflective efficiency is not a problem
in even poorly-performing headlamps. The common problems are insufficient
active optical area (lens and reflector too small), poor beam pattern
formation and focus, and low-efficacy light sources.

There's nothing wrong with nonglass, nonmetal reflector substrates *per
se*. Of course, "plastic" covers a lot of territory. Cheap thermoplastic
is ill-suited to the job, but it has been used in a great many North
American-market headlamps, because beam focus requirements are lax and it
is, well, cheap.

On the other hand, some of the very best headlamps have "plastic"
(thermoset phenolic) reflectors.

All of them use vapor-coat aluminum reflector "shiny stuff".

DS

 

Until a road rock comes along. *Krunch!* (Or lots and lots of little
pieces of road grit, which pit and "sandblast" the lens until it disperses
the light just as badly as a clouded-up plastic lens).

Hardened/toughened glass is where it's at...

 

Erm...convert lumens to watts? How, pray tell, do you plan on
accomplishing that? One might as well convert Buicks to kumquats, or
inches to volts.

There are people over on sci.engr.lighting who can explain it more
articulately than I have done.

Because "usability" is a moving target that occurs somewhere between the
light source and the fixture in which it is used. Take a look at these two
isocandela diagrams:

http://dastern.torque.net/Photometry/Cibie_CSR_Iso.jpg
http://dastern.torque.net/Photometry/Cibie_CSRH_Iso.jpg

The top one is a low beam generated by a 5-3/4" round headlamp that takes
an H1 bulb producing 1500 lumens. The beam contains 687 lumens. System
efficiency = 45.8 percent.

The bottom one is the matching high beam, 5-3/4" round headlamp that takes
the same H1 bulb producing the same 1500 lumens. The technology and size
are identical. The beam contains 856 lumens. System efficiency = 57
percent.

That doesn't mean, though, that the high beam is a better lamp, or that it
would make a good substitute for the low beam. Mostly it illustrates that
system efficiency is certainly not the only measure of system
effectiveness.

Remember also, my "usable light" definition of efficiency is only one kind
of efficiency. There are numerous others (energy efficiency,
thermodynamic efficiency, etc.)

DS

 

All of these are the same technology (coiled There are a great many
factors that go into the output of a filament lamp ("bulb"). By
dialling-in the various parameters, the light source engineer can optimize
for life, for light output, for power consumption, or (usually) for some
combination of those three. Some of the primary factors include envelope
size, fill pressure, filament diameter, filament pitch, filament wire
diameter and fill gas formulation. These 1st-order factors influence
seconary parameters such as filament surface luminance and filament
luminance homogeneity, which in turn influence 3rd-order parameters (life,
power consumption, light output) as well as 4th-order parameters
(attainable beam focus, degree and nature of uncontrollable stray light,
etc.)

Then, once the bulb is designed, its design parameters are locked in by
relevant regulations.

More info over at sci.engr.lighting

DS

 

Not arguing with the world - it can use whatever it decides to use, just
saying that if you have a choice between using *all* light (whether
useful or not) over input and using *useful* light over input, the
latter is more meaningful for real world comparisons. As I said in
another recent post, I realize that there may be some practical or
technical reasons that total light is used (for one, the meaning of
"useful" may change with application).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Thanks for the explanation. I was thinking in terms of wavelength of a
bulb - I see now that that's not it, or at least not the whole picture.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')