lux.html

My quest for light began in 1965. It was Christmas Eve, Good Saint Nicholas had dropped by. He left behind a little science kit for this 6 year old wannabe physicist. It contained some batteries, a functional and annoyingly loud electric bell, some switches, miscellaneous hardware and a handfull of small edison screw light bulbs. I was about midnight, my parents and guests has adjourned to another room leaving me alone with my batteries and light bulbs and the dark. The light had been extinguished to encourage me to leave and join the others for an evening Christmas Eve supper but I didnt care. Not only had Saint Nicholas visited that evening but the God Prometheus, the ancient giver of light, had also visited. In the dark I admired the small light from my battery and light bulb. It was was the most compelling and beautiful thing that I had then seen. I think I know how the amazing Edison must have felt some eighty years earlier. An ancient tyranny, the monster from realm of darkness had been temporarily conquered.

A perpetual light it wasnt, and by the next day the glorious little light was extinguished. The battery drain from even this little light killed it in only one night. The Lord of Darkness had returned, beaten but not vanquished.

But all that was allmost fifty years ago. Saint Nicholas returned only once more and Gods only visit you once. The incandescent light has served us well, it is extremely simple in principal and practice. Its ability to convert electrical energy to light was only bettered 70 years after its invention by the flourescent mecury arc lamp and finally in the seventies Monsanto released to the public the very first red light emitting diodes. I saved up my pocket money and ventured into town to the electronic parts place and purchased one red light emitting diode. Wow, only took 20 milliamps and put out this feeble deep red glow, just barely visible in daylight. Thirty years later again I go to town to buy one of these new fangled white LEDS. White indeed! What a load of cobblers! And EFFICIENT too! This I had to see to believe. Prometheus has been back. The result was the small hand held LED torch in this image. There are three nickle hydride batteries recovered from some long forgotten mobile phone, a switch and ballast resitors. It was an very serviceable torch. Then one day, the inevitable occured. I needed it, and in my dark toolkit was the drained LED torch. Emitting the obligatory expletive I managed without it. A little later I paused to observe that allthough the batteries were well and trully drained the marvelleous little LED was still producing light. I had not attended my toolkit for about 7 days and it had been left on that long. How much light was it producing? With dark adapted eyes in a dark room enough to read by. Then the God spoke. (Just a metaphor mind you!) Measure the current, it said, so measure the current I did. About 50 microamps. Hmmmm.

Think about that ! I added a shunt resistor to the power switch on my torch to let it have a steady drain of 100 microamps to produce a light source that cannot be put out. Its cheerfull little beacon allways beckons in the dark and produces enough light to read by. A fresh charge in the batteries gives it a full on time of over 7 days. The image here just shows the glow of the pilot in broad daylight.

Another LED torch I made to amuse the children and to show them that white light can be synthesized from red green and blue light. Try this at home. It never ceases to amaze me that the reflected light from this torch appears to contain all colors in the correct hues. Once again the power switches are shunted with 100Kohm resistors. This produces a very serviceable night light for children as well as a usefull source of light.

After a power blackout, my elderly mother tripped and breaks her hip. Just a few years ago this would have been considered the end of ones life. She recovered thanks to private health cover and a metal prosthesis. I made my parents a gift of light that they had made to me all those many Christmases ago. It is allways on, they now never fumble for a candle and matches when the power chooses to depart. It is so bright that they cannot abide it in their bedroom at night but its perpetual beacon lights the corridor nearby.

This torchs now reflects my growing ambition and lust for power . (and wealth and fame and immortality) . Only a couple of years ago a company called Luxeon releases LEDS of assorted colors with input power ratings of up to 3 watts. This torch is based on a one watt white LED and some old laptop nickel cadmium batteries. I produces a dazzling output with only 100 milliamps and a fully charged battery gives a usefull burn time over 8 hours. Naturally the power switch is shunted with a large value resistor so that I can find it in the dark. Next to do a switch mode current regulator. The 5.6ohm resistor that acts as a current ballast gets quite warm in normal operation. A significant gain in battery life could be achieved by improving this with a switchmode regulator. The next version of this power torch will have a lithium ion cell and switcher. The goal is to produce a lantern that can burn at full intensity for over a day on one charge. A solar cell on the back to keep the battery topped up would add a nice touch.

The next led torch of mine will be closer to the ideal of the perpetual light. Consider the series resistor in line with the led, the resistor only lets through the required 10 to 100 microamps required for a pilot light, nightlight. Given that from real world AA batteries we may drain nearly 100 microamps and get allmost the the shelf life of the battery anyway .What if the LED was pulse modulated to 30mA peak but 100 microamp average current. The apparent light output would provide a very usefull lantern that gives nearly the shelf life of a standard battery. Tests of mine support this theory. What I havent solved yet is a suitable pulse driver that in itself does not consume more than 50 microamps. My current circuit using a 74HC14 cmos hex trigger/inverter comes close. I used a cmos hex schmitt trigger basically to make the oscillator simple allthough this stage draws the most current because the first gate is self biased into a linear mode because of negative feedback. The other stages operating as saturated cmos switches draw essentially no static current. It produces a very acceptable flashlight beam and draws about 1mA . (Do not try this with a 74HCT14 they draw nearly a milliamp just sitting there) Next to try CD4093.

theory.
gate 12 is a simple schmitt trigger oscillator, buffered by gate 34. the high value resistor and low value capacitor provide a slight pulse delay. The 2 diodes form an equivalent OR gate resulting in a narrow pulse thats buffered by gate 98. This gate can directly drive the LED but for max optical output it drives any small power mosfet directly. The led series resister can be dispensed with after testing and design is comleted. Unused gates must be held low else the total chip quiescent current drain is higher than it might otherwise be. With these component values I measure a total average current drain of about 1mA and this results in a very bright light source. My target is to obtain a "useable" source of light that draws an average of 100 microamps which would give essentially the shelf life of a commercial disposable dry cell. The output transistor must be a mosfet, zero gate drive current and essentially zero drain source offset voltage.

And on a completely differant tangent, I do well remember the long Saturday afternoons in the sixties watching "Epic Theatre" , the old "sweat and sandles" epics. It would allways amuse me to see the heroes venturing into forgotten ancient and abondoned catacombs and sewers. How did they see ? There were allways flaming torches on the walls! I think in the the "mummy" series of B grade horror flicks, the about to be cursed archaeologist ventures into the ancient tomb. There are flaming torches lining the ancient unused corridors. What a marvellous ancient technology! A flaming torch that burns without attendance for 3000 years and completely fails to fill the ancient tomb with soot and carbon monoxide! Maybe the "curse of the mummy" was actually cabon monoxide poisoning from all those ancient flaming torches!

RGB 3 color recombination demonstration	with 100Kohm switch shunts the light is still clearly visible in daylight	at night

	one charge lasts over 12 months at this level	allways welcome in a dark room

Luxeon clone 1 watt white LED	these old cells give about 8 hours burn time

	a high gain yellow LED provides an allways on pilot light