Rectangular Tail Lights

[2bking]

A lot of builds use the rectangular tail lights in place of the factory provided round ones for a period correct look. They have an inherent design problem of not passing light in the lower half due to the corner cube reflectors imbedded in the lens. I borrowed this picture from a post on the other forum by JimmyZ which illustrates the problem. The lights shown have been fitted with a LED flat board hence the dot pattern. At night there may seem to be adequate light coming around the reflector area but in the daylight it gets washed out.
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You can see the rectangular dark area in the lens where the corner cube reflector resides. I found two designs for these lights, one with LEDs fitted in the light, the other with one 1157 bulb for the upper half and the lower half blank. The LED one still has the dark area and the design with the bulb doesn't have a reflector. The back of the reflectorless light is open to dirt/water present inside the rear wheel opening. There are plans on the forums available for a rectangular box to cover the back side but this doesn't address the need for a reflector.

I'm helping on a build that the owner wants to use the rectangular lights and have two bulbs, one for stops light, the other for turn signal. Technology has advanced in the last few years where there are 1157 LED bulb replacements available that out preform the incandescent ones. I used the iBrightstar ones shown below which run about $17 a pair for initial testing. These bulbs have a lens on the tip for focusing some of the light and have red LEDs which will have a higher lumince coming through the red tail light lens. The LEDs around the cylinder need a reflector to project the light toward the tail light lens in order to get the full benefit of the available output.
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Here is a picture of the back side of the lens showing the corner cube reflectors. They are difficult to see due to the red color.
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I milled the corner cubes down so barely a witness of the pattern could be seen and flame polished the area.
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This picture is terrible but due to the amount of light being projected and being in the red spectrum, the cell phone couldn't do any better.
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With the reflector removed the lens easily transmits the light. For those with this tail light and want to improve the output, simply grind out the reflector. Polishing will improve the output but 90% of the gain comes from removing the reflector.

[2bking]

Before I started cutting up good parts, I modeled the light assemblies in ProE to determine what could be done. I wanted to use the reflectors and bulb sockets from the round tail lights in the rectangular ones. The following modifications are somewhat simple but require a mill for the precision hole pattern needed. Two additional holes need to be drilled through the back plate and reflector which are 90* to the diagonal through the two screws attaching the reflector and same spacing. This is where the mill comes in handy but I suppose it could be carefully done on a drill press. The four holes, two new and two reflector mounting ones are used to tape a square measuring 1.90 between sides. I used a metal cutting band saw to cut the square after taping the reflector for protection. The saw cuts through reflector and housing at the sane time. The light base is brass so it cuts easily. This is a picture of the reflector and base before cutting and then cutting in progress
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I made a new lens attaching plate to replace the one that comes with the rectangular tail light. It has two 1.75" holes 1.90" apart with the outline of the part traced from the original. There are four small holes shown around the large holes but I found only needed two after rethinking the assembly.
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Using this new plate and the cut round light parts, the assembly starts to take shape.
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Another part need to be made that forms the seal around the reflectors and back. I used some .025 thk galvanized duct work sheet metal to make it. It is shown in this picture with the other new parts and modified gasket. I cut the large rectangular hole using the sheet metal housing as a guide. The uncut one is shown on the right in the second picture.
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At this time I haven't fully assembled the light because of some hardware I'm needing so no pictures are available but I have tested it and the results are very good. Here are a few more pictures of it in various assemble stages.
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[Jim1855]

Saw these at a show. Indicated at DOT approved. Thought they were very good.

https://www.rodworx.com/product-cate...60-cobra-leds/

Jim

[Big Blocker]

Quote: "I'm helping on a build that the owner wants to use the rectangular lights and have two bulbs, one for stops light, the other for turn signal."

Why not just have both bulbs (per housing) come on for both functions? Both upper and lower bulb on for brake, both upper and lower for turn signal. Individual functions in this small area aren't very distinguishable in bright light of day.
Easily do-able with current tech or some simple wiring changes.

FWIW; your issue with the original style rectangular lenses is the bottom isn't a reflector but rather a refactor lens. It's supposed to reflect back light coming at it from the outside (think headlights hitting a roadside sign).

Doc

[Cobradavid]

Why not just have both bulbs (per housing) come on for both functions? Both upper and lower bulb on for brake, both upper and lower for turn signal. Individual functions in this small area aren't very distinguishable in bright light of day.
Easily do-able with current tech or some simple wiring changes.

That's how I wired my lights (using the round lights that come with the kit). I use dual element bulbs in all four lights. Dim element comes on with driving lights, bright element comes on as brake lights or turn signal.

David

[2bking]

Saw these at a show. Indicated at DOT approved. Thought they were very good.

https://www.rodworx.com/product-cate...60-cobra-leds/

Jim

These are the ones with the LEDs but still have the reflector area at the bottom

Quote: "I'm helping on a build that the owner wants to use the rectangular lights and have two bulbs, one for stops light, the other for turn signal."

Why not just have both bulbs (per housing) come on for both functions? Both upper and lower bulb on for brake, both upper and lower for turn signal. Individual functions in this small area aren't very distinguishable in bright light of day.
Easily do-able with current tech or some simple wiring changes.

FWIW; your issue with the original style rectangular lenses is the bottom isn't a reflector but rather a refactor lens. It's supposed to reflect back light coming at it from the outside (think headlights hitting a roadside sign).

Doc

The light assemblies that are available without LEDs have a single bulb, open to the back, and no reflector for the bulb to help get the light out. So out of the box something needs to be done to protect the light on the back side. And you are right that both bulbs, if two were present, could be wired for brake and turn signal. Having only one bulb forces that but the lumens available is still poor. The bulb is vertical behind the lens so simply changing to the higher brightness LED ones only allows half of the light to directly pass through the lens. What I am doing improves the light output to the level available in the round ones FFR provides.

The upper portion of the lens is a refractor meaning it disperses light that passes through it but changes the direction. The lower part contains the reflector which works by having Total Internal Reflection (TIR) for the light coming in from outside hence the road sign reflection you mention. But physics gets in the way here where you can't have it both ways, reflection from the outside and light passing from the inside. Its not perfect so light on the back side is seen illuminating the reflector area. You have a good point about loosing the reflector but the round ones don't contain a reflector so removing the it seems to me to be the same as having the round lights. The rectangular light seems to have been purposed for trailers where a reflector is mandated. This is an issue where a lot of conversation can be generated

[Jim1855]

2bking,

From what I remember the reflex was modified or perhaps they molded it as a Fresnel. They were bright and seemed to work well and the upper and lower sections were independent or so I remember. My plan at this time is to run these.

I've done extensive testing on LEDs, although about 7 years ago, lots has changed. The reflex (the prisms) was never intended to pass light, normally it would have a metallic substance applied on the back side to form the reflector. When you light the reflex from behind you get a rectangular pattern with a lot of dark area in the middle, if lit with a multi LED in a flat disk configuration the reflex can work. A parabolic reflector should work as well. A white wall about 10 feet behind the car will tell a lot about how the lights are working.

Jim

[2bking]

2bking,

From what I remember the reflex was modified or perhaps they molded it as a Fresnel. They were bright and seemed to work well and the upper and lower sections were independent or so I remember. My plan at this time is to run these.

I've done extensive testing on LEDs, although about 7 years ago, lots has changed. The reflex (the prisms) was never intended to pass light, normally it would have a metallic substance applied on the back side to form the reflector. When you light the reflex from behind you get a rectangular pattern with a lot of dark area in the middle, if lit with a multi LED in a flat disk configuration the reflex can work. A parabolic reflector should work as well. A white wall about 10 feet behind the car will tell a lot about how the lights are working.

Jim

First, I didn't start this thread to bash anyone's product. I'm attempting to show a way to enhance the performance for those who want more from these lights, especially in the lower part.

The white wall is an excellent target for determining the intensity and pattern. I did some testing using a LED flash light and you are right about the dark rectangular pattern projected. Embedded in the dark area are some small bright spots with a pattern resembling the prism pattern. If the back were silvered, no light would come through but for cost reasons, I assume, it is not done and they are good enough for the intended application. Physics stops the light coming out the center with the prisms but it does come through around the reflector. Unfortunately, the driver behind you doesn't get a side view where the light comes through, he see a dim light. The first picture in the first post is a tail light with the LEDs trying to pass light from many directions but the dark area prevails. I think I found the same lights you are thinking about here and the lens seems to be identical to the ones I'm working with.

[BEAR-AvHistory]

Quick question, Didn't they also come with 4 tail lights?

[Avalanche325]

I do know that some had square and some had round. I got curious and found this on Club Cobra. His signature says he owns CSX2401 and CSX 3288.


Jim Maxwell
"OK, I don't want to disappoint those who knew this was coming! According to the Shelby Registry, cars CSX 3001-3200 had rectangular taillights and the CSX 3201-3360 had round tailights.
The lower "light" is actually a reflector, as stated previously. So all those replicas that are based on the S/C models should have rectangular lights. The rectangular lights were the same as used on the 260 and 289 cars. All Lucas parts, by the way."

[MPTech]

That is some great work 2bking.
When I installed my rectangular lights almost 5 years ago, I made the box to mount 2 red led panels per side. The top lights (brakes) worked pretty well, but the bottom (blinkers) were a problem in bright sunlight as you mentioned. I always thought that if there was some way to reduce the reflection in the bottom portion, this would help significantly, but I didn't have the resources to modify it properly. Earlier this year I replaced the led panels with the newer / brighter 1157 led bulbs and it was an improvement, but still not optimal.

Looks like you solved the mystery! Thanks for sharing.