Built with high intensity 8000 to 11000 mCD white LEDs, these lamps sit directly on top of a 12 volt 2.7 amp-hour SLA battery and works well on a dining room or makes a great reading light with an adjustable head angle.
The LEDs themselves are wired in series in groups of three, with each group having it’s own current limiting resistor. The resistor is chosen to limit the LED current to 20 – 30 mA at maximum voltage. In this case, absolute maximum battery voltage is about 13 volts. This is not affected by any battery charger voltage, as the lamp switch is wired to disconnect the lamp when charging.
Battery life is almost as important a concern as lamp brightness, so I settled for close to a 20 mA draw at 13 volts. A 150 ohm resistor set this just about right. At this level brightness was quite acceptable, and battery life should be at least 14 hours for the dual head lamp, and a whopping 45 hours for the reading lamp!
Well, I guess it really is time to ditch the coal oil lamps, these LED lamps are far brighter, safer, easier to use, and they produce a much nicer color of light. With the cost of high intensity LEDs dropping to bargain prices, it really is an easy decision!
I recently obtained some 21,000 mCD LEDs, and have found them to be even nicer yet. Here is a really handy, compact one-LED flashlight. It uses three AAA batteries and fits easily in a pocket or just about anywhere. A 56 ohm resistor and small slide switch mounted on a small circuit board fastened to a battery holder with some small bolts is all it takes!
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