SVOboy did a good writeup on how to do LEDs "from scratch" (using the raw LEDs, PC-Board, etc). However, for just a little more money, there is a much easier way out there now. The "trick" is that some companies (I use
http://www.superbrightleds.com ) now offer "drop in" LED replacements for standard car bulbs.
This means that many car bulbs are as simple to replace as popping out the original (incandescent) bulb, and popping in a replacement LED module exactly where the original bulb went. However, as mentioned on this page
http://www.superbrightleds.com/carbulb-notes.htm , there are still a few things you have to watch out for. For example, be very careful of light levels, beam angle, and LED color. And remember, that many OEM flasher units won't work correctly with lower LED current draw (I did indeed have to switch my flasher, before I could replace my turn signals). And (while it wasn't a problem for me), some newer cars seem to want to detect "burned out lights", and can misinterpret the lower current draw of an LED unit as being "burned out".
NOTE: In general, have the LED module color match the lens color it is behind (i.e. red LED modules, behind a red "tail light" lens, amber modules behind an amber lens, etc). Do this even if/when the bulb you are replacing was originally white, and you will be happier! The reason for this, is that a colored lens throws away a large fraction of your light, in order to turn white light into colored light. But when your LED(s) are only generating the color of light that you need, pretty much the entire light output goes through that colored lens (giving you a lot more effective light "for free", than you would get if/when you started with white light)!
NOTE: These examples are all using modules from superbrightleds.com, simply because that is what I know about (having used their modules on my own cars). But that doesn't mean you can't find another company also selling LED modules, if you look around. It's just that I happen to have usefully used the modules listed below.
LED modules I've found useful on mine (and my wife's) Hondas:
3-watt Luxeon 1156/1157 replacements:
http://www.superbrightleds.com/specs/115x-xLX3.htm
At around $20 each, these are some of their most costly LED replacement modules. However, they are also some of the brightest of the modules, and due to the lack of colored lens light losses, the red and amber versions of these are actually BRIGHTER then you will get from a normal (incandescent) 1156/1157 bulb, while turning on/off slightly quicker, and also using a small fraction of the original bulb's power (these Luxeon LEDs are actually noticeably more efficient, from a lumens/watt standpoint, than florescent bulbs!). As such, they are IMHO worth the extra cost. However, since white light doesn't have any lens losses, the white unit will still be a little less bright than the 1156/1157 it replaces.
FWIW: I currently have the red 1157 version of this bulb as my primary break/tail lights on both the CRX (two bulbs in back) and the Civic (4 bulbs in back), and it works real well (if not the cheapest way to do things). I also have two of the amber 1156 version of this "bulb", as my rear turn signals (and again, they are actually brighter than the stock bulbs they replace). In the case of the red 1157 tail/break lights, it was just pop out the old "bulb", and put in the new module. However, in the case of the turn signal lights (on the CRX), I needed to first replace the OEM flasher, before swapping in the LED units, so that the lower current draw of the LEDs didn't result in incorrect flashing rate!
WLED-5 units are nice for replacing lower light 168/194/T13/921 bulbs:
http://www.superbrightleds.com/specs/bulb_specs.htm
These units are small, and reasonably cheap (currently $2.99-$4.14, depending upon color). They are not quite as bright as a 168 bulb (much less the bigger 921 bulb), but they are pretty close (especially for red/amber LEDs, behind a red/amber lens). And, because of the way this module mounts the 5 LEDs in different angles, this unit does a pretty good job of filling the lens with light (whereas many LED units leave large dark areas on the lens, because they are too tightly focused).
FWIW: I currently use a lot of these in my cars (already making use of white, amber, and red modules). They are excellent for replacing various small lights that some cars seem to have too many of (for example, low power indicator/running lights on the car's exterior). And don't forget about using the white version of this module as replacements for your license plate lights. I even used them initially to replace my 921 bulbs in my CRX's "upper break light" (but I've since replaced the upper break light bulbs with brighter, but bigger, 921-x12 LED modules). And if I ever manage to pull the dash panel and replace my dash backlights, it is likely that I'll use these WLED-5 modules for the dash as well!
Wide angle 921-x12 modules:
http://www.superbrightleds.com/specs/T13_specs.htm
This is the module I am currently using when I want a small wedge that is brighter than the WLED-5 (above). For example, I am currently using two of this module (red version) for the upper break light on my CRX. The only warnings about this module, is the slightly higher cost ($3.95-$5.95, depending upon color), and the slightly bigger size (so it might not fit in really tight spaces expecting a 168 bulb). However, (since it has 12 LEDs) this unit is over twice as bright as the WLED-5 unit, which is why I'm currently using it for my CRX's two high break light "bulbs".
3022-x9 "Festoon":
http://www.superbrightleds.com/specs/festoon.htm
This one is currently $2.95-$4.95, depending upon color (the white is the most expensive, but also the most generally useful). I've found this unit to be great for replacing those "festoon" (clip in from the sides) bulbs in dome/trunk/etc lights, often producing more useful light than the real (incandescent) bulb it replaces. While I have white in most places, I did put a red unit in my CRX's dome light, so that a passenger reading a map/etc, won't kill my night vision (red light doesn't effect night vision the way other light colors, including white, do). And remember, that you often run car dome/trunk/etc lights when the engine is off. So by replacing these lights with LED units, you can (if/when needed) run them a lot longer without killing your car's battery.
Electronic turn signal flasher:
http://www.superbrightleds.com/flashers.htm
I think these are currently $12.95 each, and are only needed if your existing flasher can't handle LEDs, and you want to replace any of your turn signals with LEDs. In my case, I was able to successfully use the CF13JL-02/"Japanese" version of this flasher in my CRX, but only
after I removed the extra plastic around the flasher housing (as the existing Honda/OEM flasher is slightly narrower than this unit, and so this unit (while electrically correct) doesn't physically fit in a Honda without modifying their flasher bracket!!!
BTW:
Since this is a DIY post, I suppose I could sign up for a free web hosting service, and post pictures of the actual "bulbs" installed in my car. But really, I think most of us can figure out how to "change a bulb".
So the real "trick" here, is to watch out for "gotchas" (such as also having to replace a car flasher), and make sure you get the right module for the job (i.e. match the lens color, bulb layout, get a module with sufficient light and light angle). But once you do that, it is pretty trivial to install these LED "bulb replacements", and (once installed) they should last for years. And if you ever want to reverse the process, just pop out the LED module, and pop in a cheap car bulb you picked up at the store.
NOTE: You don't have to replace all the car lights "at once" (if you are on a budget, or simply find some bulbs hard to physically get to). For example, just replacing your tail/break lights (without also upgrading the "flasher") is a decent "upgrade" for many cars (since those lights burn several watts, and are on a lot). Of course, the more lights you replace, the more power you save. And don't forget, that some lights (for example, your backup lights), you don't use very often, even though they are a lot of power on those few occasions that you do use them. So it may not be "worth it" to replace rarely used lights with LEDs. OTOH once you get the LED bug, you may end up continuing on until you have virtually all the car lights (except for the headlights) replaced with low power LED lighting...
BTW:
From a safety standpoint, I recommend you spend a little more for the brighter modules, instead of trying to be cheap (and get the lower light output LED modules). After all, being properly seen, can make the difference between someone avoiding you or running into you.
But "the good news" is that if you use sufficiently bright/wide_angle LEDs, you may actually be slightly
SAFER than the stock bulbs you are replacing! This is because there is about a 1/8th second delay, while an incandescent bulb lights up (whereas a LED turns on almost instantly). This means that any bulbs that light up to tell info (such as your break lights, when you step on the break) will activate a fraction of a second faster with LEDs. And that small fraction of a second, could be the difference between a "close miss" and getting into an accident...
)? Otherwise, SuperBright appears to make a bulb-like resistor to draw the same amperage and keep the stock blinker at bay (but thus elimiating any efficiency). Safety and the "Sweetness" factor would be the advantages of an LED setup, in addition to less current draw. I can see the brake lights being a definite advantage over stock with their time to illumination. At Interstate speeds, this could even exceed the 18-feet mentioned, not only depending on speed, but the reaction time and distance of the person behind you. The cool factor comes-into the turn signal installation (I love the look of a full set of LEDs on a turn signal). I used to have LEDs in my '99 Civic and had to wire a hidden bulb to avoid the fast flash rate (tooner-style) -- I first tried using basic electronics by wiring a resistor that emulated a bulb, but WARNING, the resistor got so hot it melted the tape and plastic around it (basic electronic Physics that I wasn't privy to at the time). Later consultation with an electronic engineer pointed to the fact that I was producing a short-circuit at the temperature of 300C+. Oops. The hidden bulb worked better.
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