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LED Tail Lights, Brake Lights & Turn Signals A - ET-247A

LED "bulbs": As of this writing in late 2004, LED "bulbs" are pretty much a lost cause for the MGA tail lights. The LED "bulbs" are built to project light, with the effective projection zone being a cone somewhere between 15 and 90 degrees wide, projecting a large bright spot on the back of your tail light lens, not seen well from the side. Even with the light directed in one general direction, these lamps are still (generally) not as bright as a standard incandescent brake light or turn signal bulb. The first (and so far only) commercial LED plug-in replacement for the 1157 bulb that actually is as bright in the projected direction is 1.85 inches in diameter (and costs nearly $50). In the MGA tail light assembly the bulb mounting is in a downward direction, not pointing out the back.

Standard bulb on left -- In-line LED "bulb" on right.
This will definitely not work in the MGA, pointing downward.
Hanging LED lamp

Radiantz does make an LED unit that could work in this application. It features 48 LEDs and a hanging base, allowing positioning of the LED unit at an add angle (if you supply the support). See photo and link. The LEDs sure are cool though, being very efficient and generating useable light with very low power and almost no heat. Perhaps in the not too distant future technology will progress to allow brighter LED lamps to fit in small spaces and maybe not require the tight projection zone.

Super Bright LEDs, Inc. makes the 11157-R30-RA right angle lamp shown below left. This one may work for the MGA, as it does project light in the right general direction. I have not seen this one installed. I have considerable concern that it may primarily produce a bright spot on the back of the lens, leaving the lamp rather dim in a side view.

One often overlooked consideration is the color output of the LED. A white LED produces many colors (all colors of the visible spectrum) to make visible white light. When used for a tail light where the lens color is red, the LED should also be red. The red lens will filter out most light that is not in the red range of the spectrum. As such, a red LED will produce more light that will actually get through the lens, so the visual result will be brighter and a more rich red color (example above right).

If you would use LEDs for the MGA tail lights, there is another problem. The turn signal flasher unit requires a specific current draw (two high intensity incandescent lamps) to operate properly and to flash at the correct rate. With the very low power draw the LED lamps would function like no load at all, and the flasher unit would not flash. One apparent fix for this would be to install a load resistor in parallel with the LED lamp to produce the original magnitude of current draw. The resistor required would be a 10-watt 6.8-ohm power resistor. [It will generate 20 watts of heat when switched on, but it works on about 50% duty cycle as the lamps flash]. This would totally offset the efficiency of the LED unit. It would also defeat the safety feature where the flasher stops flashing if one bulb should burn out or become disconnected. Putting the shunt resistor in the LED "bulb" itself would also offset the efficiency of the LED unit, as well as generate the same heat as the original incandescent bulb. Radiantz makes a load equalizer (rather expensive) that can be hard wired into the system to provide the current load necessary to make the flasher unit function.

A simpler alternative is to install a heavy duty flasher unit which would flash at a constant rate regardless of the total load. This is the device normally intended to operate 4-way hazard flashers. This will blink normally with anything from one to six bulbs connected. Unfortunately this also defeats the warning function if any one of the turn signal lamps might quit working. If you do this you will need to check function of the outside turn signal lamps regularly, like every day for instance.

Having spent some time thinking about why this is not good for the MGA, I finally thought of a very good use for the LED tail light. If I were to install these things in my trailer, it would have nice bright tail lights and turn signals, and it would not affect the flashing rate of the original thermal controlled turn signal flasher unit. Hmmmm. Would I spend $100 for that?

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