About the Project
LED Lamp
The design and fabrication of this LED based lighting system took approximately 6 months from start to finish. As you may have read already, the goal was to match the light output of a 32 watt T8 fluorescent lamp while using significantly less energy. This is an ambitious task because T8 fluorescent lamps are the more efficient flavour of this technology. The LED bulbs that were designed are intended to run on sealed lead-acid batteries which means they can accept an input voltage of anywhere from 10.5 V to 13.5 V. This input voltage was chosen to make the bulbs compatible with solar or wind energy systems. This means that if your home or building is operating on solar or wind energy, you can connect these bulbs directly to the batteries and bypass the inverter. This allows you to purchase a smaller inverter and requires you to have less solar panels (due to the energy loss when converting from 12 VDC to 120 VAC).
There were two lamps created. The first contained 87 LEDs. This lamp used approximately 20% of the energy that the fluorescent lamp used. This lamp was an excellent source of light, but was nowhere near the light intensity of a 32 watt T8 tube. The second generation lamp contained 210 LEDs. This bulb was much closer to the light output of the fluorescent lamp. This data is shown on the results page. The 210 LED lamp was never connected to the current regulator due to the immense heat sinking that would be required. The 210 LED model was more of a proof of concept. This model was operated using a current-regulated bench power supply. If you are considering building an LED lamp, we encourage you to order LEDs that emit more light rather than packing more LEDs into one space. The LEDs that emit more light do not consume more energy, they are simply a more efficient diode. It is beneficial to use less diodes that can output more light rather than more diodes that output less light.
Current Regulator
The LEDs are driven with a linear current regulator that was designed specifically for this purpose. Other alternatives were considered (like a Switching Mode Power Supply), but this was the final choice due to the simplicity and robustness of the circuit. The original method of driving the LEDs was going to be a simple resistor, but this was quickly decided against. The issue with using resistors is that as the voltage drops, the brightness drops which is not acceptable in any environment. A switching-mode power supply was designed and built, but the results were not favourable so the information about that circuit is not included on this site, and there are no plans to ever release it. The switching-mode power supply was a complete failure. In the computer simulations, everything worked perfectly, but real-life tests were less than satisfactory.
The current regulator is based on the LM334 adjustable current source. The entire circuit has a very low part count (6 components) and costs approximatley 5 dollars to build (including cost for copper clad board if etching at home). A side effect of using a current regulator is that heat will be created. It was calculated that when the batteries are full, approximately 3 watts of heat would be dissipated. The amount of waste heat decreases as the battery voltage drops. The drop-out voltage of the circuit is 10.5 volts. When the input voltage approaches this voltage, the heat dissipation approaches nearly zero. Any losses are due to resistance in the circuit itself.
The final outcome of this project was very positive. While the light output was not exactly that of a T8 lamp, it was very good. This project demonstrates the ability for an LED lamp to light a room. Through visual observations, it is was an excellent source of light even though it did not output the same amout of light as a fluorescent lamp. The first lamp that was built was installed in a garage, and following lamps were actually built using the light from the first. It was an excellent source of light.
