Light Tech

Some of you may have seen this over at the RRT during their tech contest, but it’s useful here as well.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Light Tech

Here’s something that may be of interest to those of you who run early cars with early taillights.
A pair of 39's in this case, but we’ll also take a quick look at the ever popular 50 Pontiac lights.

What you’ll see is some direct comparisons to the old faithful #1157 bulb as well as candlepower listed for each bulb tested.
I probably should have taken some amp readings, but Candlepower (CP) will tell you pretty much the same thing.

All incandescent non-Halogen light bulbs were purchased at WalMart.
Which, translated, means you can get them at most places that sell auto oriented bulbs.

All CP readings were taken from 5" away in an attempt to preclude ambient light from having an affect.
All CP readings were on the taillight circuit.
CP read was directly from the bulb with the red lense removed.

Voltage for the lights was sourced from my pickup parked nearby.
It’s a 2002 Ford F150 SuperCrew and has a large capacity battery.
Along with that, the taillights on the 31 were fed with 8' of 14 gage wire which comes close to approximating the typical taillight wire length and size in most hot rods.

Voltages noted with each photo pair were taken with a digital voltmeter connected to where the taillight wiring was connected to the source wiring.
An 8' long single 14 gage ground wire was run and connected to the right side taillight body.
The 31's body is primered steel fwiw.
As is obvious, the taillights and stoplights would have been 5% - 8% brighter if the engine was running, but voltages with the engine off were fairly close so test indications compare favorably with one another.

Before we get too far along, a comment on what some vendors call "Bright Bulbs."
It would be interesting to see what these actually are, but imo they’re nothing more than a bulb designed and manufactured to reach it’s rated maximum brilliance at a lower voltage than the usual auto combo taillight/stoplight bulb.
Bulbs that fit a particular socket or receptacle are manufactured in many different voltage ratings.

When I worked at the power company it was common for newbies to stick a 24 volt bulb into a 48 volt socket.
The results were always interesting, either a bright flash or a growing brilliance for 2-3 seconds until the bulb blew it’s filament.
Other way round, a 48 volt bulb in a 24 volt socket would barely glow.
When a slightly lower voltage bulb was installed into a higher voltage socket, light bulb brilliance was sufficient and they lasted a long, long time.
The bulbs of differing voltage ratings were used as indicator lights so a loss in brilliance didn’t
affect things too much.
It would be interesting to see just how long Bright Bulbs last.
Imo, not as long as a standard bulb.

Want a house incandescent bulb that’ll last a long time?
Buy bulbs rated at 130 volts instead of the more common 120 volt bulbs.
Available at Home Despair and like places.


The garage - where the pics were taken - has all lights off and it’s somewhat dim in there.
In other words, not quite as bright as shown in the pics due to the camera tries to make up for the lack of light.
The camera - a small digi-cam by Canon, Model #A540 - had the flash turned off for all pics.
Sorta like early dusk in the garage in a manner of speaking.

This first photo shows four of the lights we’ll be testing.
Set up in a home-made fixture.
I thought we’d get some good comparisons here, but in the pic all the bulbs look about the same.
All bulbs on the taillight circuit.
Bulbs used (left to right) 1157, 1157LL, 2057 & 2357LL
I believe the LL stands for Long Life.



Photo #2 showing three bulbs - also on the taillight circuit - are (left to right) 1157, P21-5W & a 5 watt Halogen.
The Halogen bulb available at Bob Drake re-pro parts.
It’s a well made unit and will stand a bit of handling compared to some of the fragile looking double Halogen bulbs on one base.
Like always, if you want the Halogen bulbs to last, don’t touch them with your bare fingers.
Latex gloves seem to work well and the original pair of Bob Drake Halogens I had in the 32 lasted 3-4 years before one of them failed.


As you can see, the Halogen bulb throws a lot of light.
Seen in the pic and also seen in CP readings . . . more on that in a bit.


The photos will be self-explanatory to an extent.
Additional things listed will be bulb type, CP (CandlePower) and voltage.

Keep in mind the left taillight will be the one with differing bulbs.
The right taillight will run a standard #1157 bulb as supplied by Bob Drake who also supplied the 39 taillights . . . which are very nice lights.

The first photo of the pairs posted will be taillights and the second photo will show the stoplights.


This first pic in the series has a P21-5W bulb installed.
Voltage = 11.94
CP = 10




Photo pair #2, 2357LL bulb installed.
Voltage = 12.34
CP = 9




Photo pair #3, 2057 bulb installed.
Voltage = 12.26
CP = 5




Photo pair #4, 1157LL bulb installed.
Voltage = 12.24
CP = 6




Photo pair #5, Halogen bulb installed.
Voltage = 12.02
CP = 70 - not a misprint, 70 is the CP.




Photo pair #6, 1157 bulb installed, a match both brand-wise and age-wise to the 1157 bulb in the right side taillight.
Voltage = 12.27V
CP = 9




Here’s a small bonus to see how the popular 50 Pontiac taillight compares to the 39.
Visual only, no voltage or CP readings were taken.
I did this test because my pal’s full fendered 29 roadster with Pontiac taillights - with blue dots to boot - look brighter than the 39 taillights in my 32.
And in fact I bought a pair of Pontiac taillights - sans blue dots - with the thought that I’d have a nice bright taillight.

I was surprised to see the Pontiac taillights were about the same size as the 39's and brightness seemed the same.
Both the Pontiac and 39 taillights in these photos have black painted buckets.

To top it off, my pal’s (equipped with the original 1157 bulbs) has a black painted bucket as well.
My 32 has a bright silver painted bucket.
Paint used was "Chrome" as noted on the label and it’s pretty reflective.
Even so, Digger Dave ran some tests some time back and reported that white paint has the best reflectivity as measured by his light meter.
It’ll be white paint for me whenever I can get to it.

Here’s the Pontiac vs the 39 taillight.




Most of you probably know this, but when you buy re-pro Dietz or King Bee headlights as utilized by A’s, 32's etc. they usually come with a standard seal beam light.
For about $9. you can get a Halogen sealed beam at WalMart that’s a direct easy to bolt in replacement.
Same plug etc.
The difference in light between the two styles is flat amazing.


I learned a few things about light bulbs during this little investigation.
Some bulbs do better than others, but the Halogen bulb is the hands down winner.
I understand the Halogen bulb pulls 5 amps and the standard 1157 pulls 1 amp on the taillight circuit.
Fuse your system accordingly.
Use adequate size wiring as well, 14 gage should do it for most of us.

One thing I think would help extend the life of the Halogen bulbs would be to vent the taillight housing.
Early car housings are quite small compared to the large taillight housings found on modern cars and heat doesn’t dissipate as fast as it should.
To that end some kind of filtered air exchange device would help to extend the life of the Halogen bulbs.
Filtered to keep dust out of the housing.
If dust is allowed in, the taillight’s light output will be diminished.
Lots of ways to do it so I’ll leave that part to your imagination.


Over the years I’ve seen some beautiful cars that were equipped with too-small taillights.
Sorta asking for it to an extent.
It behooves us to use as bright a light as possible and as large as is aesthetically pleasing.
The cars we run are usually small, many times with dark non-reflective - read flat - paint and they’re difficult to see.

The third stoplight is a viable option and a good idea imo.
I have one, rather ugly and billety, but I think it’s saved the day more than a few times.

A good looking third stoplight is easy to set up so it’s bright and blends in with the lines of the car.

More on that another time....

 

Your TECH posts are a MUST read Jay!
Excellent info and presented professionally as always.
Thank you!

 

thanks a good tech

 

White paint...I have read repeatedly that this is best. Anyone know why??
And--I have heard that contrary to intuition, flat white is most bestest...true?? Why??
Actual chrome is known to have very poor reflectivity comp[ared to siver or aluminum. I read a tech explanation of this, but it hurt my head...
Crome paint: WTH is in there?? Aluminum as the filler??

 

Nice work. There is a HUGE difference in candlepower with the Halogen! Hmm, perhaps I need to get my bulbs changed.

 

Halogen bulbs are certainly brighter; I have run them for years on my roadster. I think there is a substantial safety advantage there.

One downside to note is that they have an adverse effect on stoplight switches. I think a relay will fix the problem, although I have not developed enough ambition to actually rewire using one...... Changing switches isn't that hard, LOL.

On my truck, I recently went to LED taillight bulbs. They seem to be pretty bright, even through the stock glass taillight lens, and have the added advantage of pulling almost zero current. They don't look exactly the same as an incandescent bulb, but the key task is keeping the drooling illiterates from running into the back of the old truck......

 

Very neat information, and thanks for sharing. I'd like to see the LED comparrison to what you've already shown, as those were what I was contemplating on my Dubble A truck.

As for the white being the most reflective, I believe it is because the color white is the absence of color, so it doesn't absorb any colors, therby reflecting everything back. On the opposite end of the color spectrum, black contains every color, which is why it absorbs color.

Think of it like this... large bodies of water appear blue because that is the only color that is reflected by the waters surface, and all other colors are absorbed. Also, think about the differences of wearing a dark colored shirt in the sun versus wearing a white shirt. The dark absorbs the heat more while the white will help dissipate it better.

 

You have just shown with great research and clarity what I have been "preaching to the choir" for years. Good job, maybe more folks will wake up to the problem and get those little bitty lights brightened up.
Good ground, a clean lens(inside and out), 2357 bulbs(what I always use), and a white painted interior of the lamp. That work worked so well on my son's 57 BelAir everyone at the car shows who saw the tail lamps wanted to know how he did it. He told them and over the weeks and months many cars were showing up with much brighter tail lamps and stop lamps!
AGain, good job!

 

Great tech Jay!!!

 

[quote=
As for the white being the most reflective, I believe it is because the color white is the absence of color, so it doesn't absorb any colors, therby reflecting everything back. On the opposite end of the color spectrum, black contains every color, which is why it absorbs color.)

Actually, white is all the colors reflected together, I guess that is why the white backed lights appear brighter, and black is the absence of reflected light.

 

I went back to this to get the addy to add to another post on lights and ended up reading through it.
I would guess the stoplight problem is a hydraulic stoplight switch and not the GM underdash style.
I used one of those on the 32.
No probs in 14 years and that includes 2-3 years of Halogens.

 

Another cheap thing to do, if your tailights don't have a reflector, is cut an X in aluminum foil & pop it over the bulb. Reflects a lot of light!

 

I think another aspect of the white vs silver reflector is that with white, the bulb lights up the the entire surface of the reflector, meaning that white reflects the light in all directions.

The silver reflects the light in a straight line. Angle of incidence equals angle of reflection, so any part of the reflector that's not at the correct angle between your eye and the bulb's filament appears darker when silver because that light goes in whichever direction it's reflected. Those off-angles appear brighter when painted white and likewise appear brighter through the lens.


As for burning up brake switches.. If you add a relay, you can omit voltage from the switch altogether by putting it on the ground circuit of the relay and running the other side of the switch to ground. Run your hot wire to the relay's Batt+ terminal with a jumper to the trigger terminal. Attach the brake light wire to the relay's output and you'll never burn another switch.

 

Great post, glad it popped back up.

White reflectors, regardless of candlepower reflected, work best for one other reason- They produce the "reddest" illuminated lens. Silver or foil reflectors make the lens more of a translucent red that's not as plainly noticable.

 

A little fwiw - and I don't want to get into the ammeter vs voltmeter bit here - if your ammeter is fairly low scaled (mine is 30+ & 30-) you can make a quick check to see if the stoplights are working ok.
Just watch for deflection to the minus side and see if it's about the right amount for all three stoplights . . . or two.

Came in handy when 5 year old granddaughter kicked the fuse cap on my underseat panel and the cap unscrewed and backed off far enough to kill the stoplight circuit.

I check all the lights by looking in store window reflections at night when parking or pulling out of a parking place . . . along with doing a walk-around once in a while.


The addition of a relay is a good idea.
It'll help to get full voltage to the light.
Something to think about if you have some long run's of wire.

 

Now the white...flat or gloss?? I've always heard flat, but why??
I tend to paint anything that gets clean enough blkack, so I don't want to buy two flavors of white to experiment...at least I've figured out that flat black isn't right for the reflectors.

 

I think flat white is more PURE... and doesn't 'absorb' light like a glossy white would.....