I Want a General Guide to Headlight Design

[Ken_McE]

I'd like a better understanding of the general principles underlying headlights, how they project light, and how well they work over all. Anybody got suggestions for a beginners reference?

Some things I've been wondering about:

* Are there inherent advantages to larger or smaller lights, say a one inch round light vs. a four-inch, vs. a six inch?

* Any inherent advantages to square vs. round lights?

* Any inherent advantages to using more weak bulbs vs. fewer strong ones? say a line of ten ten-watt bulbs vs. two fifty-watt bulbs?

* What's the deal with projector vs. reflector lights? What are their relative strengths, weaknesses?

Inquiring minds want to know...

 

[Hamilton Felix]

I am no expert, but I'll say headlights vary greatly. In general, bigger is better; more reflector is better. We see the ordinary sealed beam incandescent lights of the past, halogen sealed beam, halogen removable bulb, halogen projector, HID projector, etc.

Although size and shape were once governed, today's headlights have to meeting lighting standards but can be "styled" to suit the car/truck/motorcycle.

A row of lower wattage lights might put out the lumens of one larger bulb, but you'll have a hard time focusing that light into a useful beam.

I just threw this out there to start the discussion rolling. I'm sure there are others who know lot more.

It seems to me that with dual element lights, such as the H4 headlights on my motorcycle, the designers work hardest to get a good low beam, with sharp top cutoff and even fill. The high beam has to come from the same lamp, but its shape doesn't seem to be the highest priority.

 

[-Virgil-]

Pretty good article on Wikipedia, with lots of refs to follow and learn more. Also buy this book (Yes, it is seriously worth at least that much money), and this one (average the price of the two books and they're both completely reasonable).

 

[Hamilton Felix]

Hey, that's great stuff! And if your budget is really tight, you might get lucky and find that first book in a library.

I've never understood why American cars with "stacked" headlights put the low beams on top the high beam on the bottom...

 

[-Virgil-]

I've never understood why American cars with "stacked" headlights put the low beams on top the high beam on the bottom...

Because until recently, it was a requirement: Low beams on top in a stacked configuration, low beams outboard in a side-by-side configuration. The latter is still required, but the former no longer is. The idea is to maximize the range of the low beams, which is done by maximizing their height. There have been glare problems with high-power headlamps (and the U.S. beam photometry and aim standard does a relatively poor job of glare control), hence the dropping of the "low beams on top if stacked" requirement. The "low beams outboard" requirement is to make sure the width of the vehicle is made as apparent as possible at night. Pretty flimsy reasoning, though, if you ask me. There are parking and marker lights to mark the width of the vehicle. This requirement together with the rounded front-end shapes of today means a high-performing but deep low beam optical package can't be used, so a lower-performing but shallower optical package is substituted. European (rest-of-world except North America) regulations have no such requirement and they seem to get along just fine.

 

[tay]

Well, it's important for the lowbeams to be outboard so that the turn signals can be a 1.5" round amber light immediately inboard and adjacent to the headlights, so that you won't be able to see the turn signals at night.

 

[Hamilton Felix]

Thanks, Scheinwerfermann.

The idea is to maximize the range of the low beams, which is done by maximizing their height.

Sounds like something a goverment regulator would come up with. With the nice sharp top cutoff of the low beam, the lower we can mount them, the more horizontal and parallel to the road we can aim them, without blinding oncoming traffic. Of course, when this was first written, American sealed beam headlights threw such fuzzy "puddles of light," that it's a stretch to refer to "beam patterns." Perhaps angling those downward was the only option.

 

[tay]

yeah, IMO for something with a sharp cutoff, I think a nearly level low-mounted headlight would give better distance lighting and less foreground than a downward aimed high-mounted headlight.

 

[-Virgil-]

With the nice sharp top cutoff of the low beam, the lower we can mount them, the more horizontal and parallel to the road we can aim them

Keep in mind according to U.S. specifications, all headlamps of a type are aimed alike, regardless of their mounting height. That is, all VOR headlamps are aimed with the cutoff at the horizon, and all VOL headlamps are aimed with the cutoff 0.4 degrees (0.7%, 2.1 inches at 25 feet distance) below the horizon...whether they're on a Corvette or an F550 Super Duty.

 

[MichaelW]

low beams outboard in a side-by-side configuration. The latter is still required, but the former no longer is... The "low beams outboard" requirement is to make sure the width of the vehicle is made as apparent as possible at night.

Are you sure the low beams mounted outer is still in effect?
Because the new '10 Lexus RX350 has the low beams mounted inboard.

 

[-Virgil-]

Are you sure the low beams mounted outer is still in effect?

Yup.

Because the new '10 Lexus RX350 has the low beams mounted inboard.

Naw, it only looks like it (but it certainly does look like it!). It's got BiXenons. I'm not sure if the outer lamps are even hooked up in the American-market cars. The next question, of course, is if the BiXenons' placement complies with FMVSS 108. The same question can be asked about the Mustang's sequential turn signals. If the standard is strictly read, the answer is probably "no" in both cases. But nobody at NHTSA is particularly interested in reading the standard any more strictly than it takes to say "the manufacturer asserts compliance and we have no plans to investigate or challenge that assertion."

 

[MichaelW]

Some neighbor got one. I am pretty sure the DRL is partial intensity, outer mounted halogen reflectors.

So that is the crux of the matter, if the halogen high beam function is omitted for the US market, then it is legal, insofar as '"the manufacturer asserts compliance and we have no plans to investigate or challenge that assertion."'

http://www.pressportal.com.au/news/451/ARTICLE/4382/2009-02-18.html
I found it interesting, that some people bitched enough that Toyota would put blue tinted halogen bulbs so that would match the bi-HID color temperature.
in the 'WORLD CLASS EXTERIOR VISION FOR RX 350' section [basically at the bottom]


and regarding the Mustang 'caricature of a turn signal, instead of an actual NON red turn signal', it could be worse if it went ON-ON-ON & off-off-off, conveying a directional vector (I've seen that on a fire truck, but in amber, and with a sideways chevron arrangement of LEDs)
At least it goes ON-ON-ON, and then off in unison.


another addendum, if the high/low mount requirement is no longer in force, why didn't GM mount the low beam of the Silverado and Sierra-closer to the ground? Do they think it is 'macho' to blind people.