Backlit Mirror

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Even if LEDs were invented back in the 1962 and they were embedded in every electronics since then, the era of the cheap and durable lighting began only in the 2000s, when the manufacturing process of white light emitting diodes became so cheap, that everybody could afford it. The inefficient regular incandescent bulbs were replaced quite fast with LED bulbs, that are not only more durable, but also have a lower power consumption than the old filament-based ones.

What about PL tubes ? These were used quite for a a long time, but due to the fact that for the wattage, it offers only half of the illumination level (lumen) than the LEDs and they also contain toxic mercury, which is poisonous to the living world, therefore it must be disposed with great care.


LED light sources can be found these days in lot's of forms : light bulbs, PL fluorescent tubes, led strips, etc.

Usually, to achieve at least 1000 lumen to be comparable with regular incandescent bulbs, the manufacture combines more than one LED diode. In case of a led-strip, the LEDs are placed at a distance of 3-4 cm from each other. In order to achieve the desired illumination level, one must calculate how many LEDs he needs. Most of the time you will be limited by space, therefore you will use a led-strip whose length fits into the place where it will be mounted.

Step 1: The Idea:

Ok, so the idea came at one of my friend's place, where I first saw such a backlit mirror in the bathroom. I've liked the way the light "came out" at the edges, from behind the mirror, illuminating the wall behind it. It really did look great.

First of all, such mirrors can be found everywhere, therefore it's easier and even cheaper to buy one.

However, I already had this mirror, it was perfectly good, so why throw it out ? Also, it had plenty much distance between the wall, therefore it could house a small power supply and the LEDs without a problem.

Step 2: Preparing the Parts

Before de-mounting the mirror from the bathroom wall, let's have a short list what part you are going to need:

  • LED-strip. Based on the mirror's size, it can be between 3-5 meters. Of course, in case of a bigger mirror, first you will have to calculate the length you will need. Pay attention to the temperature (cold white, normal white, warm white). In bathrooms usually cold light looks better, but it's really up to one's taste. There are LED-strip types that have a silicone cover. This one is better, as it will protect the components against corrosion, as you will place it in an environment with high humidity (bathroom).
  • Power supply: Make sure the power supply can handle the current the LED strips will need. The current will increase with the length of the strip. Usually, the manufacturer specified the current consumption or wattage per meter. Also the supply voltage is important. To convert the Wattage to current, use the following formula: W = V * A (wattage = supply voltage x current). Pay attention to the supply voltage of the LED-strip. Usually it's 12V, but one can find also 220v or 24v. The 12V is better, as you will use it in humid environment. If not necessary, why use a higher voltage?Also, if possible, get one rated IP68, but at least is should be splash-proof, at least.
  • Cables: You will have to cut the LED-strip in order to be able to make the sharp turns at the corners.

Tools:

  • soldering iron, copper
  • thermocontractable tube: this will be used to insulate the wires after soldering

  • glue: the LED-strips are self-adhesive, but not always. Therefore it won't hurt, if additional glue is being used.

  • protective gear: as you were soldering, protective eyewear is highly advised.

Step 3: Cutting the LED-strips

Carefully measure the mirror you have and try to imagine how you are going to place the LED-strips in order to get the best results. It's not ok to place them right at the edge, as in this case it could be deranging if you look at it from the sides. Placing them too deep, or close to the center is also not ok, as in this case, you will loose the nice glowing effect as the light reflects from the wall behind.

So the best is to place it 3-4 cm from it's edges.

Also, calculate that the 2-wire cable needs some place to be able to bend. 4-5 cm would suffice.

Very important! When you cut the LED-strips, pay attention at the markings. Usually it's next ot the + and - signs and they have the 2 copper pads exposed. Cut them right in the middle, so you can solder both parts.

To be able to apply them parallel with the edges, it doesn't hurt if you place some marks on the backside of the mirror.

Step 4: Soldering

Soldering the LED-strips should not be complicated. First, make sure, in case it's coated with a silicone layer, this should be removed before soldering. Otherwise, the iron will melt the silicone and not only it will smell bad, but it's also toxic and will get in the way of the lead.

Carefully pre-solder the pads on the LED-strips, the small cables that you will use to connect the LED-strips you've cut at the previous step. Make sure, when soldering to respect the polarity. In case your cable has color markings, usually the red wire shall be the "+" , the black one the "-". In case the cable is black, one should have a white marking, this is usually the "-".

After soldering, apply the thermocontractable tube (cut 3-4 cm) and then with a heat gun (or lighter) heat it up so that it shrinks to the cable, making a perfect insulation.

After each part is soldered together, try it with a power supply and carefully check the power consumption. If your calculations were correct, it should not exceed the maximum power that is written on the power supply.

In the picture above, the total power consumption of the LED-strips is around 0.5A and the power supply is rated at 1.0A. So it shall be good.

Warning:

1) Never exceed the maximum load supported by the power supply, even if it says it's current is limited. In case of a cheap supply, it can lead to overheating and risk of fire and damage.

2) Always insulate the + and - poles with thermocontractable tubes, and make sure the don't move. In case the 2 poles are connected, this will lead to short circuit and overheating of both the wires and the power supply.

Step 5: Applying the LED-strip and Testing the Circuitry

Even if you've followed my instructions and carefully checked the circuitry after every LED-strip was soldered together, after applying the LED-strip to the mirror (you might need to use glue as well), make a final test and carefully observe the total consumption. Again, this should never exceed the maximum current rating of the power supply.

Also carefully observe that each strip lights with the same intensity and all LEDs are working. If it's not the case, re-check the soldering and make sure you did not damage the LED-strip during the operation.

Warning: It's advised to use a power supply like the one in the picture for test, that has settable current limit and also can measure the voltage level and current consumption. Always start with the current limitation set at minimum, and then gradually increase it until it doesn't limit any more, but never exceed the calculated theoretical value.

This needs and explanation:

Let's say you've calculated that all of the LED-strips will have a current consumption of 0.5 A. In case you supply the circuitry, and you observe that your current limit already exceeded this and the power supply is still limiting the current, this means that somewhere you have a short circuit and you will have to re-check the wiring. Raising the current limit above this can lead to damage of the wires, LED-strip, etc. So it's better to double check again than regret later.

Step 6: Connecting the Power Supply

As the final step, if everything is ok, then we can connect the power supply.

First, it should be glued to the mirror, or you could use self adhesive tape that is adhesive on both sides. Also note, that the red-black wire is the output and the blue-brown is the 220V input.

Warning! Never exchange them! Doing so will damage both the LED-strip and the power supply as well.

Also, respect the polarity: red is the +, black is the -, while the brown is the live wire, the blue is the null.

After soldering the wire, make sure you insulate them properly (take special care to the high voltage part!) and test the circuitry, this time connecting the brown and blue wires to the power socket.

Warning! Make sure you don't accidentally touch the high voltage, as you will get yourself electrocuted.

In case everything is done properly, all of the LEDs shall be lit nicely.

Now it's time to re-mount the mirror. You will have to connect the 2 supply wires (the brown and the blue ones) in parallel with the existing bulbs that are mounted in the bathroom. Make sure you cut down the power by lowering the fuses and also check with a voltage detector pen that you don't have hazardous voltage.

Make sure that you do also here proper insulation. If it's not possible to use the thermocontractible tubes, you can substitute it here with electrical insulator tape .

Once everything is in place, check again the wiring and then you can raise the fuses again.

Step 7: Conclusion

The backlight of the mirror gives a futuristic look to your bathroom. If you've followed carefully every step, this setup will work for many years.

As for future development:

Instead of one-color LED-strip, one could use a programmable RGB strip and an ESP8266 microcontroller:

https://blog.hackster.io/build-your-own-wi-fi-led-...

This opens lots of new possibilities to customize the lightning in the bathroom: custom lights based on the time of the day, would be the first that came to my mind: cold white in the mornings, warm white in the evenings.

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