slantsixdan said

Here's what to know about LED retrofit bulbs in vehicle signal lamps (brake lights, tail lights, parking lights, turn signals, etc).

First, the quick nutshell version:

• Answer to "Will it work?" is more complicated than it seems.

• Fundamentally different kind of light source, so unlike with filament bulbs, physical fit doesn't guarantee optical compatibility/acceptable performance.

• Giant mountain of unsafe junk on the market, all fraudulently hyped as an upgrade.

• A few legitimate products that work OK in some of the lamps they fit in; important to check the actual function carefully.

• Optical compatibility isn't the only issue; there's also electrical compatibility and thermal concerns.

Now the long, detailed version:

Start with how signal lamps (parking lamps, turn signals, side marker lights, brake lights, tail lights, reversing lamps) have to work. It's a lot more than just "Yep, that lights up and looks good to me". Please see this post—I point you at it not to say "Forget any bulb retrofit, you're going to have to build from scratch", but just so you get some idea of the complexity involved beyond "Yep, it lights up and looks good to me".

Bulb-type lamps (brake light, tail light, parking light, turn signal, side marker, whatever) rely on a point source of light, a glowing filament, that radiates more or less equally in all directions—a sphere of light—collecting and distributing that light with optics in the lens and/or reflector. A group of LEDs, in whatever formation, can't exactly duplicate such a sphere of light at the required scale, so the light distribution from bulb-type lamps equipped with "LED bulbs" is often seriously degraded.

Disregard all the trinkets and garbage that aren't from reputable, major-brand light source suppliers. All the junk on eBay, all the trash from ReallyBrightLEDs.com and SuperKewlBlingLights.com and all the rest of it.

LED substitute bulbs from legitimate makers have been evolving in a good direction, in fits and starts. The first generation Sylvania Zevo product was a pathetic, completely unsafe sick joke, disingenuously marketed as "for interior and off-road use only" (yeah, because gosh, there are just all kinds of vehicles where red 1157 bulbs are used in the interior…). The second/current generation Zevo product, with its aluminum Y-frame design, has a whole lot more and better engineering behind it.

Philips used to offer a few bulbs (1156 and 1157 red; 1156 white) that had two emitters back-to-back on a metal sandwich-board kind of arrangement. Those were very good, and compatible with a lot of different lamps. So of course Philips discontinued those; now they offer two different bulb families that are both inferior to the older design and both incompatible with a lot of old-car lights.

The few legitimate LED bulbs that exist work well in some of the lamps they fit in. In others, they work poorly. Their performance has to be carefully assessed in whatever particular lamp they're installed in, by comparing them side-by-side with the original incandescents as reasonably well described (in an accessible DIY manner) here.

And in some lamps, including a lot of old-car lamps, they don't work at all, because all the legitimate LED retrofit bulbs have only rear/side-facing emitters. That works in some lamps with a reflector bowl behind the bulb to gather and magnify the light, but there's a whole other kind of lamp that doesn't use (or doesn't only use) a reflector bowl. Instead, these lamps have what's called Fresnel-type optics, the kind where the lens has a central magnifying area directly in line with the filament of the installed bulb, and spreader optics surrounding that magnifier. Often the magnifier is a round bullseye and the spreaders are a series of round prismatic rings surrounding the bullseye, but sometimes the magnifier is square or rectangular and the surrounding prisms are linear. If there's no light directly out the front of the bulb, there will be minimal to zero output from the lamp.

Those previous-generation Philips bulbs i mentioned put out enough frontward light to work in many Fresnel-type lamps, but the current Philips products put out none. Unfortunate, but that's the world we live in.

There are the thermal issues with LED bulbs. Unlike with previous light sources (light and heat emitted together through the lens of the lamp), an LED puts out light from its front side and heat from its back side. The light goes forward, the heat goes back. As the LED heats up, its light output drops (it's called "droop"), so each LED must have an adequate heat sink to carry the heat away from the emitter and prevent it heating up high enough to drop the output low enough to put the lamp's output below the minimum requirement. LED vehicle lamps (designed and engineered as such) have to pass tests for output maintenance with prolonged operation, because that's a real-world situation (stuck in traffic with foot on the brake, tail/parking lights operating for hours on end, etc). This is a challenging requirement for even legitimate LED lamps, and it's a really difficult challenge for such a thing as an LED bulb, because there's a very limited amount of space for any heat sinking, and all of it's going to be inside the lamp there with the heat-emitting LEDs—there's no way to use outside air to cool the LEDs unless you have a big honkin' rear housing on the LED bulb. There are some out there like this, and they create physical-fit problems (not enough room behind the lamp for the big honkin' housing) and other issues related to improper fit in the bulb hole. The point of all this is you can't just throw a big pile of LEDs at it to sledgehammer the optical compatibility issue, because then you run into other problems.

Then there are electrical issues. There's a legal requirement that a turn signal bulb failure must markedly change the flash rate—much faster or much slower—so the driver will be alerted the failure (no such requirement for brake lights, though; fun, eh!). The outage-detection works off bulb continuity and resistance, and in those terms LEDs behave very differently than filaments. So installing LED bulbs typically results in the turn signals flashing much faster than the legal requirement of 60 to 120 flashes per minute (or flashing not at all, depending on what kind of turn signal flasher you have). This is not a big deal on older cars like ours; you just upgrade the turn signal flasher to this one (2-prong like original; connect its ground wire conveniently).

Finally, there's another matter that affects the compatibility of LED bulbs with lamps designed to use filament bulbs: most white LED bulbs are high-CCT ("cold white"), like 5000K, 6000K, or higher. That's cold/blue-white light. These white LEDs produce very little red in their output, unlike a colourless filament bulb. Put a cold-white LED behind a red lens, and you get a dim, muddy, pinkish-brown light that's way outside the boundaries of what's allowable as red (and invisible to people with a common form of colourblindness). This is a bad idea, as we're talking about lights that are supposed to immediately convey the vehicle's position/direction of travel and that it's decelerating. Messing with their colour, intensity, and light distribution makes them unable to do their job keeping you from getting hit. Just yesterday I was in traffic behind a Honda with an OE-type filament brake light bulb on the left, and a white LED on the right. The OE-bulb side was much brighter and redder (the light worked better with the stock-type bulb).

A '66 Barracuda has reflector-type tail lights, not Fresnels, so after you clean the reflector and repaint it (hardware store "chrome" spray paint is ideal), try these in the brake lights, subject to the comparison performance test linked earlier in this post. You might get lucky with these in your backup lights. There is no legitimate LED bulb compatible with your Fresnel-type front turn signals, so this won't work; you'd have to either leave them alone (brighten them up with these; 25% brighter than stock) or try your "luck" with the LED-bulb trinkets and trash, again subject to that same performance check.

Dashboard bulb LED upgrade is easy and doesn't make problems if done thoughtfully; see here.

Headlamps: again, a mountain of fraudulent/unsafe junk on the market, including all "LED bulbs" that fit in halogen headlamps (see here) and a whole lot of toys shaped like whole sealed beam headlamps. But there are some good-to-excellent ones on the market, too. Right now the bang-for-buck item is this one, made reasonably well in Taiwan by Maxxima and sold by Tungsram, which is the new name for GE Vehicle Lighting. (if you want to buy it under Maxxima's own brand, you can, but at 4× the price!).

Beyond that, the Peterson 701C is pretty good, and so is the Truck-Lite 27270C. By a big, big margin the king daddy of them all is the JW Speaker 8700, which comes in black or chrome. All three of these are well made in America. There's a lot of lookalike copycat junk "recommended" when you look at these; ignore them.

Whatever headlamps you wind up using, the most important thing about them is how they're aimed.

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