In this Instructable, I will show you how to build an LED desk lamp from scrap materials. With the exception of the LEDs, wires, and other components, you can get the other materials for free. Depending on where you get the parts, you can build it for under $5. Typically, a 3 watt LED lamp costs $20. This lamp uses about 5 watts which is a good replacement for compact fluorescent lamp.
In this project, you will learn how to build an LED lamp from a metal can, wire hanger, plastic board, wooden plank, and some electronic components.
Step 1: Materials and Tools
3 - 1 watt warm white LEDs
N-channel MOSFET (IRF540) and NPN transistor (2N3904)
1.33 and 100k ohm resistors
26 gauge wires
2 screws and 2 bolts and nuts with washers
12V power supply (9V transformers may give you 12V)
Corrugated plastic board
Wide can with metal base
Sanding tool or tool sharpener
Step 2: Prepare the Lamp Shade
When selecting a can, make sure the bottom is metal so that it heatsink the LEDs and current regulator. The bigger the can, the more wattage it can handle. Feel free to try 3W LEDs. With a 15 cm wide can, the temperature did not exceed 40°C after running the lamp continuously.
Trim the can
The lamp shade requires cutting the bottom portion of the can, leaving two inches of its height. The trimmed edges should be filed and folded with a plier. Do not cut yourself while doing this. It is much safer if you can find a shallow can like a cookie tin so that you can avoid this step.
Mount the LEDs and MOSFET
To mount the LEDs and the MOSFET, apply heatsink paste to the centre and epoxy to the outer edges. Firmly press them onto the flat area of the can and let it set for a few hours before soldering soldering.
Step 3: LEDs and Driver
Solder Three White LEDs in Series
Select a Power Supply
White LEDs have a forward voltage of about 3.5V. For three LEDs, the forward voltage would be 10.5V and the power supply should be 12V. If you are using old transformers, a 9V transformer may give you 12V when the current is low.
Build a Current Regulator
I was about to use the LM317 regulator to reduce the parts count but the dropout voltage was too high. I used the MOSFET current regulator instead and I was able to build it without a circuit board and used heatshrink tubing to hold and insulate the parts. Epoxy was used to glue them to the can.
You could use the LM317 if you increase the power supply voltage but there is a very good chance that you can add 1 more LED if you are using the MOSFET driver.
For the current regulator, I selected 1.33 ohm for R3 and the current was about 0.42 A. Always check with an ammeter.
Add a Switch
Drill a Hole on the Can
To keep the power cord in place, drill a hole on the can for the cord. With the cord through the hole, add enough hot glue around it.
Twist Loose Wires Together
Step 4: Lamp Stand
Cut a Piece of Corrugated Plastic Board
It's up to you to select the height of your lamp. For my lamp, the dimensions were of the plastic board was about 30 cm by 5 cm.
Reinforce the Plastic Board with a Wire Hanger
Since the plastic piece is very flimsy, it should be supported with two pieces of wire hangers on both side leaving room for the screws and bolts. This will also allow you to bend it so that the light is directed where you want it to be. For a 30 cm piece, one hanger is usually enough. You will have to straighten the hanger with a plier and put it through the holes of the plastic board. To cut the hanger, bend it several times while holding it with a plier. The ends of each piece should be bent so that they won't fall out.
Build the lamp stand
Find a plank of wood. I used a 15cm by 9cm by 4 cm plank here. To build the stand, screw the plastic board onto the side of the wooden plank. When screwing onto a plastic board, it is a good idea to use washers to keep them from sinking in.
Mount the Lamp Shade to the Stand
To mount it to the stand, drill holes onto the lamp shade near the power supply wire and use nuts and bolts to secure them.
Step 5: Cost of Materials
Approximate Price of Each Item
3 - 1 watt LEDs=1.40
Resistors and transistors=$0.50