Early electric headlamp history, and modern LED's

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Luke
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Early electric headlamp history, and modern LED's

Post by Luke » Sun Nov 28, 2021 9:49 pm

Headlamps, or at least electric headlamps and retro-fitting LED light sources appears to be a common topic on this forum. There can be quite a divergence of opinion around LED's particularly, and people often cite a number of different sources to support their view.

One of the issues regularly discussed results from the widely divergent designs of LED light sources, including the misapplication of 'bulbs' designed for tail-light use (where 'end' light output can be more important than side) or, not uncommonly, manufacturers not understanding headlamp design requirements and producing 'bulbs' of dubious practical use. The latter may be done in an effort to obtain greater overall light output from a high number of small runout LED sources - more is better, right?

Well, no, not necessarily; and so that you can make a more informed choice with regard to headlamp light sources I thought it worth briefly discussing headlamp design fundamentals, with particular regard to the early 20th century. For the purposes of this discussion I'm concentrating on the typically Model T headlamp with 'fluted' lens, although the short explanation below will give some background to other headlamp design.

The Model T fluted lens headlamp is an optical system that combines two properties to create the desired light beam cast. These are Catoptrics (reflected light through the use of a mirror), and Dioptrics (the refraction of light through the use of a lens), together this makes the Model T headlamp a Catadioptric system. For those interested in ancient history it's likely that Catoptrics preceded Dioptrics by several hundred years, but it's not until the 19th century that the two really combined to make an effective system. The French were early experimenters here, but in my view it was only around the time that the Stevenson's began their remarkable period of lighthouse construction that things developed sufficiently to set the stage for comparatively high-performance and easy to use T headlamps in the 1910's.

With a T headlamp you have a source of light, originally intended to be from a small V-shaped tungsten filament, that is applied at a specific place within a curved reflector that, when adjusted correctly, will project a relatively round focused beam outward. This utilises the catoptric principle, it provides a reasonably bright beam, but it can be dazzling to oncoming traffic, and will usually not give a laterally broad enough light coverage for the driver.

Enter the fluted lens. When applied to a working lamp the vertical flutes act as lenses and will widen the original catoptric focused beam sufficiently to improve the lateral spread without losing focus or increasing the beam height. Later lens still can often have a combination of differently formed lenses in the glass so as to provide an even more controlled beam output. The Ford Model A is such an example, as is the ubiquitous 7" sealed beam headlamp of later years - by comparison the Model T headlamp lens is very simple thing - but not ineffective all the same.

As well as the optic system itself light source design has developed over time. The original V-shaped tungsten filament bulb was a 6V 30-odd 'candlepower' device that required a reasonable amount of current to operate satisfactorily. They were specified (see SAE Handbook, Vol1) as having a light centre of 1 1/4" +/- 3/64", as measured from the centre of the filament field to the bulb side of the lock pins in the base (of the socket). The specification goes on to say that the longitudinal axis of the lamp filament at the focal point shall not deviate more than 3/64" from the axis of the lamp base.

These dimension limits were required to standardise bulbs such that they would provide a suitable output at the correct focal point of a typical paraboloidal reflector then in use. The resultant beam should have little spurious light spill (ie. it should be as near 'round' as possible), and be sufficiently 'powerful' with the then somewhat limited light source.

In later years I've noticed that some tungsten filament bulbs in use have not had the requisite V-shape, meaning a dimensionally different light source than originally specified, and more recently people have utilised a variety of LED bulbs, some of which have an extremely broad light source, often both along and orthogonal to the bulb axis. Some may also have a thin optically impervious plane, either side of which is mounted a (light emitting) diode or two. It should be clear to the reader that both the 'incorrect' tungsten bulb, and many LED 'bulbs' will lead to an imperfect Catoptric derived beam, that in turn can affect the output of the system as a whole when the glass lens is added.

How imperfect, and whether it is of consequence will depend upon several factors. Primarily, from an oncoming driver's perspective, the beam should not spill upwards strongly enough to dazzle them, and for the driver of the source vehicle they need a beam that has good breadth and cast, and is sufficiently powerful enough to provide good illumination of the road surface and surrounds. Given that many LED light sources will have significantly greater light output than a traditional 32CP tungsten bulb it perhaps matters less from a beam intensity perspective that their light is often cast from greater area, however this can affect the 'perfectness' of the beam and through rogue light rays from the reflector and refraction from the lens may spill sufficient light to bother the oncoming driver. Thus in choosing a LED lamp there are several things to note:

  • Try to obtain a unit that has as narrow a light source as possible - ideally it should output ~1.25" from the pins, and be of limited width.
  • When trialling a LED lamp it's best to focus with the lens off. This goes for tungsten-filament bulbs as well.
  • LED's can be very 'white' or 'cool' (i.e. they have a high temperature). It's best perhaps to select bulbs with lower temperatures, around 2800/2900K is a good number. That said many modern headlamps operate successfully at higher temperatures, however drivers may complain they're too 'bright', or 'they don't look right'.
  • Although it's difficult to provide a direct correlation, there are simply too many variables, bear in mind that the original 'candlepower' measurement was a somewhat crude measure and is no longer used. Nowadays LED's are often rated in lumens and, without wanting to get into pages of discussion, you could crudely say that a 400-lumen LED lamp will have similar light output to say a 32CP tungsten filament bulb (L = CP * 12.57). This gives a guideline at least.

Finally, this post is just intended to go over some rough points and provide basis for informed and informal discussion. It's certainly not exhaustive, nor is it a scientific article - particularly given I've left a lot out and tried to avoid too much esoteric 'stuff' (and some of it is opinion) - and indeed parts may even be contentious, but hopefully it'll be of interest to some. As a matter of further interest and useful record I also include below some relevant pages from the Bureau of Standards Motor-Vehicle Headlighting circular No. 276 of 1925 - no doubt the fluted lens displayed will be recognisable!

Luke.

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Topic author
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Re: Early electric headlamp history, and modern LED's

Post by Luke » Sun Nov 28, 2021 9:50 pm

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Re: Early electric headlamp history, and modern LED's

Post by Scott_Conger » Sun Nov 28, 2021 10:33 pm

Nicely done
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Re: Early electric headlamp history, and modern LED's

Post by JohnH » Tue Nov 30, 2021 7:09 pm

It does seem that the modern day poor reputation of Model T headlights is largely due to incorrect bulbs, and reflectors in poor condition. The repro incandescent bulbs I've seen don't have the filaments in the correct position either.
When the optics are set up properly it makes a huge difference. I'm using 6V LED bulbs now, which are designed for headlight use in parabolic reflectors, and I won't be going back to repro incandescent bulbs. For one thing, high and low beam actually work as they should. A very well written article - thanks for posting it.


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Re: Early electric headlamp history, and modern LED's

Post by TXGOAT2 » Tue Nov 30, 2021 7:12 pm

Do yo have a source, brand name, and part numbers for the LEDs you are using?

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Re: Early electric headlamp history, and modern LED's

Post by JohnH » Wed Dec 01, 2021 12:12 am

TXGOAT2 wrote:
Tue Nov 30, 2021 7:12 pm
Do yo have a source, brand name, and part numbers for the LEDs you are using?
The bulbs I used came from here http://www.classicandvintagebulbs.com/page6.html However, it seems the supplier now provides a different model of bulbs to what I am using.
I show how they look in a post here https://mtfca.com/phpBB3/viewtopic.php? ... 7358#p7358

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Re: Early electric headlamp history, and modern LED's

Post by Steve Jelf » Wed Dec 01, 2021 11:47 am

The last time I checked, LED's were usable in a battery/generator system with its stable voltage, but not in magneto lights with their fluctuating voltage. I wonder if that's still the case.
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Re: Early electric headlamp history, and modern LED's

Post by Luke » Wed Dec 01, 2021 2:40 pm

Steve,

Technically, since a number of LED lamps are rated at 5-20V they should work reasonably well, however I've not tried them on a magneto myself, and you'd need to ensure they were polarity independent (ie. they have a built-in rectifier). Not hard to address if they're not polarity independent - given LED's are very low current draw I'd just rectify the common supply, and include a decent capacitor to smooth out the ripple (which may be evident, given that LED's are also quite 'fast' cf. incandescent). Add circa $5 and 5 minutes to the job.

With luck it may be that Max will be in a position to tell you you more, if he tries out some on his car soon.

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Re: Early electric headlamp history, and modern LED's

Post by Chris Bamford » Wed Dec 01, 2021 5:14 pm

Thank you Luke, for a most educational post. Much appreciated.

One big take-away for me is the instruction to focus the headlamps with the fluted lenses removed. Makes perfect sense and it's on my to-do list.

On the subject of LED bulbs, I run them on my '24 Speedster with mixed feelings... on the pro side, they are considerably brighter than the previous filament bulbs and of course draw less power. As this car is often driven after dark, occasionally on the highway and frequently at higher that typical T speeds, the pros win out. The two negatives are firstly the colour (too white for my liking and I don't recall any colour-temperature choices at the time), and the 'Dim' setting biases the beam to the right, rather than down. I assume this is a result of the base pins being indexed 90° off where they ought to be.

Photos below: Incandescent vs LED light bulbs shining on brown cardboard; Speedster lighting... the driving light is a 6-volt H6006 halogen sealed beam in a T headlamp bucket, with both filaments wired to come on when the T headlamp switch is on Bright. I've switched around the headlamp wires Bright vs Dim at the socket, therefore Dim on the switch is Bright on the bulb (with driving light off) and Bright on the switch is Dim on the bulb (thus biased to the right) plus High & Low on the driving light.

24T Incandescent vs LED.jpg
24T Old guys looking.jpg


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Re: Early electric headlamp history, and modern LED's

Post by MichaelPawelek » Wed Dec 01, 2021 5:47 pm

Chris, Tell is about that cool motometer!

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Re: Early electric headlamp history, and modern LED's

Post by Chris Bamford » Thu Dec 02, 2021 1:44 pm

MichaelPawelek wrote:
Wed Dec 01, 2021 5:47 pm
Tell us about that cool motometer!
It's a British Calometer, as fitted to a great many Morris cars and others +/- 1930. Common over there but very much a rarity here.
A bit more info and some links in this thread:

http://www.mtfca.com/discus/messages/17 ... 1300120785


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Re: Early electric headlamp history, and modern LED's

Post by Luke » Thu Dec 02, 2021 6:22 pm

Appreciate the comments on the post, thanks.

Just to further the history behind all this, to a very limited extent, it's perhaps of some interest that much of the work behind eventual legislation (at least in the U.S.) was carried out by members of the Illuminating Engineering Society (IES) and the Society of Automobile Engineers (now the Society of Automotive Engineers or SAE).

It is clear, in reading early journals of these two organisations, that much research and experimentation around vehicle lighting was carried out in the 1910's particularly, and to a lesser extent in the 1920's. They were not blessed with the accurate equipment we have today, nor did they have the more universal standards we have now and as such a fair bit of work went into developing means of measurement as well as actually on the [head]lamps themselves.

Colour/temperature of light was understood but was a developing field and (as I read it) reasonable proposals for standardisation were only coming up in the mid-1910's, and means of measuring intensity were many and varied - and not especially rigorous in some cases. Indeed the early determination of an individual lamp intensity (measured in candlepower) simply relied upon human perception of that lamp casting against a 'standard' lamp.

In addition to these hindrances it's apparent that different States handled the 'issue' of vehicle lighting quite differently and although my knowledge of U.S. history is fairly limited I understand that it's only when the Bureau of Standards delivered their 1925 circular that there was a common law or standard to follow. No doubt that came about through the extensive efforts of members of the IES and SAE in different States working together via their societal journals. In particular the IES 'Transactions' are, er, illuminating; the following is an example of 1918 from New York:

ies_jul_18_vehicle_headlamps1.png

This page was a random choice out of many, it's an extremely condensed summary of that particular approach to vehicle lighting. For a more detailed example of the attempt to iterate towards a common standard you could read the 1919 Report of the 1916-1917 Committee on Automobile Headlamps here (downsampled to fit here and with thanks to the University of Toronto and the Internet Archive):

ies_1919_rpt_16-17_committee_headlamps75.pdf
(7.42 MiB) Downloaded 36 times

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Re: Early electric headlamp history, and modern LED's

Post by Luke » Thu Dec 02, 2021 6:34 pm

To provide some further information on focusing; from 1921 here's a useful IES paper from Mr Grondahl on headlamp adjustment with regard to glare:

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grondahl_focus_1921_d.png

Finally, while I don't know for sure how different jurisdictions handle the assessment of old vehicles, in this country at least such vehicles are (generally) measured against the standards of the day. Thus they cannot be expected to perform as well as a modern vehicle, and will not be failed as a result. To that end I believe it's useful to have a working knowledge of these early standards, particularly if faced with an official who is oblivious...

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Re: Early electric headlamp history, and modern LED's

Post by Novice » Sat Dec 04, 2021 2:50 pm

Steve. The ledlight.com wedge light works on a/c and dc from 6 to 30 volts. should work on a mag and maintain close to the same brightness at all engine speeds from idle to high speed. The headlights wiring must be changed to parallel instead of series. a better method is change to 6 or 12 volt led bulbs and use the mag for charging the small ignition
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battery. if You lose Your mag You will not be in the dark on the long drive to OCF.

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