From Physics Professor: Wait -- where are your numbers/calculations for LaserSaber's 5 HOUR run with TWO LED's running from a 1000 uF cap? I don't see these. Yes that's because I did not include them (though I did the math). I just did a little groundwork hoping the guys would also make some additional measurements besides just runtime. I thought LS used a 3300 uF and 9 volt battery (which can be over 10 volts fresh) Maybe I didn't see his latest. This would give around 165 mJ. NOTE: He just taps the cap with a 9-V battery, so less than 9V in the cap at the start is likely... But conservatively, we can take 9V in the cap, then the stored energy is: The capacitor will charge very rapidly considering the low internal resistance of the (Alkaline) cell, 150 to 300 milliohms. With the higher value and using a 3300uF cap, you can estimate approximately one time constant (63.2%) per millisecond. It would be very hard to guess how long he taps it, best to try it yourself, but a 4 mS tap gets you 98% of voltage. Currently I am doing some light measurements using a very sensitive Photodyne light power meter to quantify actual light power output. One test I did reduced the duty cycle to about 1%, measured power input was kept at 0.009 mW yet the LED looked to the eye as if it were being driven with the higher 0.033 mW level. Note that this is far below the 0.1 Watt rating of the LED The LED's at the threshold of visibility can be driven with a very sharp narrow pulse where the average power is extremely low, but the peak power is much higher. The problem is it may shorten the LED life and rapidly degrade it's light output.
« Last Edit: 2014-05-19, 00:55:22 by ION »
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