LED Lamp Design
This is the page you have been waiting for. Here you will learn how to build your own LED based lamp that can be installed into any bi-pin fixture. You will be creating a 4 foot fluorescent lamp.
This page outlines the assembly of an LED lamp. One of the components you will need is the current regulator. This page gives a schematic and the basic operating principals behind it.
Before reading, please take a glance at the materials list to see what is involved. Most of this bulb can be created with parts that can be picked up just about anywhere, but consider ordering the LEDs online, you can save a great deal of money.
Assuming you have all of the supplies infront of you, lets get started!
Step1: Cut Your Plexi-Glass
This step is relatively simple. A standard fluorescent tube is approximately 48 inches long and 1.5 inches wide (T12 = 12 * 1/8 inches wide). Take your sheet of plexi-glass and cut a piece that is 1.5 inches wide by 44 inches long. 4 inches is left in the tube for the current regulator and wiring in the ends. This is best done on a table saw while wearing all appropriate safety equipment. If you do not have access to a table saw, consider using a plastic laminate scoring knife, shown below.
Step2: Mark the Surface of the Plexi-Glass
This step is also relatively simple, but must be done with a high degree of accuracy. You may need to adjust this step slightly to accomodate the tools you have available to you. To mark the surface of the glass, the strip of plexi-glass was clamped to a dry-wall "T" as shown below. Then using a utility knife and a general-purpose square, the marks were created. The dry-wall "T" used had fractional-inches marked on it, so they were used as a guideline as to where to create the marks. The first step in marking the glass is to go across the shortest side of the plastic, marking at regular intervals widthwise. Then the marks were created lengthwise. These second lengthwise marks could be omitted if extra car is taken in the next step if you want to make your plastic as mark-free as possible. The final product is shown below. This step is more of a general guideline. Your process will almost certainly differ. If you are marking holes for 87 LEDs, you will be creating 29 rows. This works out to approximately 1 3/8 inches between groups if starting 1 1/2 inches from the end.
Step3: Drill your Holes
Its now time to drill the holes. This process is best done with a drill press. If you are creating an 87 LED bulb like the one designed, it will take approximately 20 minutes to drill all of the holes. Grab a piece of scrap lumber and clamp it to your drill press's stage. Align it to be square to the drill press stage, and the correct distance to ensure that all of the holes drilled fall in the same plane and on the score marks. The ideal drill bit size to use is 3/16 inches. This size is slightly smaller than required but allows the LEDs to be mounted without glue. This is where you can omit the lengthwise score marks by ensuring the jig is clamped in the correct location. Below are pictures of the process.
Step4: Mount your LEDs
Its now time to mount the LEDs. Grab your bag of LEDs, and insert three into a row. Ensure that the polarity is kept constant. All of the positive sides (longer lead) should be on the same side of the plexi glass. Next using needle-nose pliers, bend the leads into a square as shown in the picture below. Next, solder the leads together. Repeat this process for the other touching leads. The resulting soldered connection should be enough to hold the LEDs in place. Trim off any excess lead, but leave the main (+) and (-) long as shown in the picture below.
Step5: Add Resistors
Next, grab your bag of 2.7 ohm 1/4 watt resistors. Trim one side of the resistor down to 1/4" and trim the (-) side of the LED triplet down to 1/4". Solder the two shortened leads together. Repeat until all of the LEDs triplets have a resistor. The reason this resistor is 2.7 ohms is due to the current regulation circuit. The LM334 (the main component in the current regulator) has a reference voltage of 64 mV. A simple ohm's law calculation can determine this resistor value.
If you would like to change the current running to the LEDs, simply adjust this calculation.
For more information about this, check the regulator page.
Step6: Add Power Rails
Take some 18 AWG copper wire and being to solder it in place along the sides of the LEDs. Leave approximately 4 inches of extra wire on each end to work with at the end. Assuming you are starting with the positive rail, hold the copper wire against the LED's lead just slightly above the flattened area. This flattened area is a small "warning" that soldering below it can damage the LED, so try and stay above it. Now that the copper is held against this spot, fold the lead over the copper wire and solder. If you are bulding the 87 LED model, repeat this process 29 times until all of the LED triplets have a tie to the power rail. Then repeat this process for the resistors. The resistors do not have a "safety mark", so try and remain at least 1/4 inch away from the resistor when soldering. The image below is a cross-section of the lamp to help you layout the resistors and power rails. You will notice a 10 degree angle on the LEDs in this cross-section. This would be an ideal design that could make the lamp usable without a diffuser. However, this angle is not a requirement. It is difficult to drill accurate angles in the plexi-glass. In the bulbs that were built, the angle was omitted and the holes were simply drilled straight through.
The circuit is wired in a series-parallel circuit which allows for "power rails". The idea is that the LEDs are in series to use as much as the available as possible without going below the drop-out voltage of the LED. (3.5V * 3 = 10.5 V) Then, clusters of 3 LEDs are wired in parallel to get the necessary current to each LED.
Step7: Create Bi-Pin Connectors
A Bi-Pin Connector is the most common type of connector used in fluorescent lamps. The bi-pins commonly used have 12.5mm between two rigid pins. To create these connectors, take a piece of scrap wood and drill two holes approximately 12.5mm apart. It helps to use a drill press and digital caliper, but it can be done with a ruler and hand drill. The depth of these holes is not important, make them at least 1/2 inches deep. The holes should be 1/16 inches in diameter. Cut two 5 cm pieces of 14 AWG bare copper wire. Insert the two pieces into the drilled holes. Slip the end cap from the tube protector over the two wires now stuck into the scrap wood. Twist the two loose ends of the wire together ensuring that the other ends remain in the scrap of wood. Prepare some low-temperature melting plastic. This is usually done by simply boiling some water and pouring the granules in. Pour the molten plastic into the end cap making sure that the plastic is at least 3/8 inches deep and distributed evenly throughout the cap. Allow the piece to cool and when the plastic is fully cooled and hard, remove it from the wood. Trim the two wires coming out of the end cap to approximately 3/8 inches. You should now have a replica bi-pin connector that can be slipped into the end of the tube protector with no effort at all. Repeat this process to create another end-cap. When you have two completed, mark one as positive and the other as negative using a marker.
Step7: Install the Current Regulator and Attach the Bi-Pin Connectors
Build a current regulator as per the plans located on the "current regulator" page. The LED mounting plate should now be populated with LEDs, resistors and power rails. Slide the mounting plate with all of its components into the clear tube protector. One side of the PCB for the current regulator has three holes. Connect the loose ends of one side of the power rails to the two outer holes on the PCB ensuring that the polarity is correct. Take a short piece of wire of any gauge and connect it to the first LED triplet between the resistor and the (-) side of the LED. Connect the other end of this wire to the center hole on the PCB for the current regulator. This is the "tap" used to regulate current. The next step is to take a short piece of 18 AWG wire and connect the positive bi-pin connector to the remaining hole on the current regulator PCB. This will be the input trace. Take the negative bi-pin connector and connect it to the negative power rail on the opposite end of the tube. This is the rail with the resistors installed. Trim all wires to be as short as possible. The final step in creating the LED lamp is to slide everything into the tube and slip the bi-pin connectors into the ends. Ensure that the bi-pin connectors are aligned with each other.
You just created your very own LED lamp! To test your new lamp, connect a 12V 1A power supply and bask in the beautiful white light. This is not the ideal way of connecting it. Please remember that this lamp is intended to be operated on a solar system or a large switching mode power supply operating many of these lamps to lower the overhead.
If you like this project, consier getting friends together to build them. The best way to make these lamps is on an "assembly line" with at least two people. One person can be installing LEDs and mounting resistors while the other adds power rails.
You are also free to add more LEDs to this lamp! This circuit can handle up to 2x the amount of LEDs installed here, but it is important that you heatsink the power-transistor appropriately. You may also want to consider cutting vent holes to allow the passive cooling to be more effective. The heat issue is not a problem for the components. The power-transistors have an operating temperature of up to 250 F, but the clear plastic tube protector does not.
Check out the pictures page and enjoy!