Car Interior From Tungsten to LED




About: I am a University of Edinburgh electronics engineering student.
Have you ever wished that your overhead interior light was brighter helping you find your dropped stuff. This instructable will show you how to easily improve the conventional interior light using some new age tchnology.

Why would I do it?
  • It's more energy efficient - uses less energy and generates less heat
  • It's much brighter than the standart bulbs
  • It's more stylish and makes your car look better
Is it expensive?
  • No - you have to invest in one metre of LED strip that costs less than 10EUR
Is it complicated?
  • No - you need some basic soldering skills and nothing more
  • The lifetime of an LED element around 50,000 to 100,000 hours, so you won't have to worry about changing the LEDs in five years or so

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Step 1: What LED to Use?

There are ready made lights that fit to the bulb holders but I wanted to use some LEDs that come in strips.

Resistors are mounted on the strips. Every three LEDs can be separated from the strip and connected to a 12V supply.

Step 2: Light Housings

There were four light housings in the car that I am showing here. You will probably have to use only your hands to take off the housings or maybe a screw driver to loosen some screws.

Step 3: Prepare the Housing

Try and fit as many LEDs as possible. I managed to fit 2 pieces each with 3 LED elements on it, making it to 6 LEDs for the smallest light housing.

The metal bulb holders are bent to allow me to fit the new LEDs.

Step 4: Shape Out a Plate for the Back of the LEDs

The strips have some glue on the back that allows them to be easily put on some flat surface. 

Shape out a metal plate that fits in the light housing. It is also needed to take out the little heat that the LEDs generate.
Aluminium is easy to cut with these metal cutting scissors.

Step 5: Soldering!

There are two wires that you need. A wire for the positive path and a wire for the negative path. If you cut a strip into smaller strips, you will have to reconnect the terminals the right way. Positive to positive and negative to negative.

Put 12V to the ends and test it!

Step 6: Glue

Use some liquid glue (or hot glue) to glue the wires. You can skip this, but I am sure that there will be vibrations on the whole thing and some glue is not bad.

Glue the metal plate to the housing.

Step 7: Solder the Power Supply

Finally solder the positive and negative wires to the original bulb holder metal parts. 

There may be such a case that you will have to measure the +ve and -ve terminals on the car connector, but for me there was no difference as from the car's roof the connectors could be put to each side of the light housing.

Step 8: Finish the Rest of the Light Housings

The rest of the lights are made in the same way. One you get it, it's pretty easy.

The two housings that look the same already had a metal plate in the construction, so I decided to glue the LED strips onto them without cutting separate metal plates.

Step 9: Perform a Test!

Here is the final result going over some tests. Just plugged the 12V power supply.

Step 10: Put the LED Lights in the Car and Enjoy

LED Contest with Elemental LED

Runner Up in the
LED Contest with Elemental LED

Fix & Improve It Contest

Finalist in the
Fix & Improve It Contest

Hurricane Lasers Contest

Participated in the
Hurricane Lasers Contest



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    30 Discussions


    7 years ago on Introduction

    Overall, nice instructable. Very creative use of the LED strips. As an experienced automotive LED guy, I usually cringe when I see automotive and LED strip mentioned together. That being said, I actually really like the idea to use them in this situation. They are perfect for an application like this (short on times, lower heat environment, non-safety critical, etc.). They also dramatically simplified your wiring and the amount of soldering that you had to do. Are there better quality options? Of course, but they require sourcing better LEDs, cutting perf-board etc. This is a great idea for a beginner.

    There are a few things that I feel I should mentioned having a lot of experience in automotive LEDs:

    First off, those LED strips are designed for 12V. Unfortunately, automotive electrical systems run at somewhere between 12.6 to around 14.5V depending on the vehicle model/is the system charging/etc. Second, automotive electrical systems are EXTREMELY noisy. It is not at all uncommon to see very short spikes in the 20-50V (or higher) range as inductive loads like relays, fans, electric motors, solenoids, etc. switch off and on. These short spikes can kill LEDs over time. They are often part of the cause for the dead LEDs that you see on tail lights even in OEM vehicles.

    First lets discuss the overvoltage problem. Since the supplied voltage fluctuates between 12.6 and 14.5V you are basically over-driving the LEDs. At 14.4V, you would be running them at 150-180% of their rated current causing them to dramatically heat up. Since the resistance of LEDs decreases as they get hotter, you will eventually enter thermal run away and the LEDs will die. Even if we assume the vehicle only runs at 12.6V you are still running them at 115-120% of their rated current. This is drastically shortening the life of the LEDs. If you want me to get into the math, I can.

    Now this isn't all doom and gloom. There is a simple fix. You simply need to add resistance to the array to balance things out. You have three options: The first one is you can replace the 150ohm SMD resistors with 270ohm ones. I'm not a huge fan of replacing SMD parts so your next option is a better one in my opinion. You can insert a single resistor before or after the array. The value of the resistor will vary based on the number of strings used but a simple trick around the calculation is to just use parallel 120ohm resistors. So if you had a single 3-led set just use a single 120ohm resistor. If you had dual sets (like shown in this instructable), parallel the 120ohm resistors. If you had three then triple and so on. This is easier that calculating the needed resistor and finding it.

    Now if you do the above your LEDs will likely last for a year or two if not more. If you want to really improve upon this then we need to take care of the voltage spikes as well. The easiest way to do this is to use a voltage regulator. Because the currents used here are very small you can use one of the tiny transistor sized (TO-92) regulators. Use a standard 12V regulator such as the LM317 (in the TO-92 not TO-220 style) and this will take care of both of the above issues in one go. No need to add resistance and the regulator will filter out the large voltage spikes. Ideally, you would want some stabilizing capacitors before and after the regulator (you actually have to if you use a low dropout regulator), but since space is a premium you can omit them unless lacking them presents a problem.

    Personally, if it was me I would just do the resistors because it is the easiest and takes care of 95% of the issues. This is not in a safety-critical location so if the LEDs fail then at worst you are without a dome light for a few days. If this were a taillight or turn signal then a voltage regulator is a MUST!

    2 replies

    Reply 3 years ago

    I wish I had even a tenth of your automotive wiring / electrical knowledge.

    I love (LOVE) extra lighting in cars, but I'm relegated to hunting down a garage / bodyshop / whoever(?) to install anything I want.



    7 years ago on Introduction

    this project is impressive. I am wondering how it affects your night vision while driving? that is usually the reason why lights are restricted on the interior of a car. please use caution as joggers and other people not wearing proper reflective materials may be harder to see while using these interior lights.. This may also cause problems with your car insurance if a modification to your vehicle causes bodily harm or property damage as a result. I love the design and will see if i can apply a dimmer function to the design.
    thank you for the amazing idea.

    6 replies

    Reply 7 years ago on Introduction

    Interior lights should not be used while driving, no matter what kind. Passenger side map light etc may be OK, but if you are driving and need to look at something in the car closely enough that you need the light, you are going to be distracted enough to cause an accident whether the light is bright or dim.


    Reply 7 years ago on Introduction

    I agree, the interior lights are primarily used when the vehicle is stationary and you do not need to look at the road as you would if you were driving.

    Having these LED lights inside the car won't cause any damage I suppose.

    About the dimming: The car has a dimming function that is part of its electrical system. When changing the lights from bulb to LED there is still this dimming that you can see when the lights power down from 100% to 30% of their luminosity. The rest of the 30% do not dim, they switch off immediately and this is because the LED is a diode that has a voltage drop on it and it won't operate if the voltage that you apply on it is less than this voltage drop. So when the voltage drops from 12V to 0V you see the dimming effect until it reaches 1V or 2V or whatever the diode voltage drop is.


    Reply 3 years ago

    I ordered some LED interior direct replacement bulbs off of ebay.

    They worked, but they were no brighter (like, at all) than the original incandescent ones---just a whiter colour.

    That being said, I have heard that there are a wide range of quality and brightness in these replacement LEDs, so just because mine were dim, doesn't mean another manufacturer's might not be brighter. The problem is you have no idea how many lumens they put out before buying, And even if the seller states a lumens output, how do you know how many lumens your original bulbs produce?

    This seems like a way brighter idea.


    Reply 7 years ago on Introduction

    Yes this is all good and yes, you save time and money, and I could replace the stock bulbs the same way. Now it feels much more different for me personally.


    6 years ago on Introduction

    PedroDaGr8, I agree.
    Anyways direct driving LEDs is bad, and I can't stress this enough.
    LED can make wide swings in their Currents for just a few Milli Volts.
    Cree XM-L, Takes 1 Ampere at 3V... but goes a full double 2A at 3.3V.... now thats very sensitive. I bet at 14.4v your LEDs are getting 2~3X their rated power and are on the way to dying early.

    PedroDaGr8's Suggestion aside, i would suggest going for an Single 3W led (eg Seoul P4 driven at 700mA) and use DC-DC constant current sources. They take in anywhere from 11~16v and provide regulated outputs, and they're small enough to hide. You'll have to think about the Heatsinking tough.

    1 reply

    Reply 3 years ago

    Yes and no. His might be...but there are LED strips that are rated to 12volts.


    3 years ago

    You can also add to "more" that if you accidentaly leave the light on overnight, It won't drain you car battery...


    6 years ago on Introduction

    Awesome i have found some uses for those in the house as well!!!


    6 years ago on Introduction

    Good job. Nice instructable. I done this to my truck last summer when i couldn't keep light bulbs from burning out quickly. Turned out to be a wiring issue, but its good now. The LED really brightens up the interior.


    7 years ago on Step 5

    Am I wrong or shouldn't the LED's in the lower portion of this picture be turned 180 degrees to mirror the top LED's in relation to where the resistors are ?

    3 replies

    Wow this didn't end up where I posted it. Well it's the one showing the LED's laid out and wired up with 2 sets of three LED's.