SHOWALL FUN PRANKS HIGH VOLTAGE LAZARUS-64 PHOTOGRAPHY SPY GADGETS VIDEO GAME
Figure 6 - The LED pulsing circuit keeps the duty cycle to a minimum
Figure 6 - The LED pulsing circuit keeps the duty cycle to a minimum

Once you have the timer part of the circuit built up, you can check the output on an oscilloscope, if you have one. Without any LEDs connected, take a reading from the output of the 555 timer on pin #3. The output should look like the one shown in Figure 6, with a frequency near 1.5 kilohertz and a pulse time of around 10 microseconds. This extremely short duty cycle will ensure that the LEDs do not fail from overheating. The fast frequency of the pulses will make the light look continuous to both video cameras and the human eyes. For comparison, a TV remote control pulses the LEDs at 40 kilohertz and drives them up to a similar current level as this circuit does.



Figure 7 - The three pulsed LEDs are brighter than the single non pulsed LED
Figure 7 - The three pulsed LEDs are brighter than the single non pulsed LED

The three LEDs shown lit up in Figure 7 are running from the pulsing circuit, whereas the single LED is running from direct current though a current limiting resistor. Although it is difficult to tell in the image, the three LEDs running in pulsed mode certainly seem brighter to look at and there is an amazing shift in color from pure green to greenish blue. This effect was unexpected and surprising considering all four LEDs are exactly the same model. To ensure that I did not have a mismatched LED, I replaced the single LED with one of the pulsed LEDs, and it was confirmed that pulsing this green LED caused a massive shift in color from about 500 nanometers (pure green) to somewhere around 470 nanometers (green-blue).

While doing a little research on how this bizarre color shift was happening, I found that a few other experimenters have found that sharp pulses to LEDs can alter their wavelength. Apparently, 450 nanometer blue LEDs can be forced to output ultraviolet light by doing this, so this opens a few doors for future experimentation.

Overall, the results were fairly obvious to the naked eye that the pulsed LEDs were definitely brighter than the non pulsed LEDs, even if I only drove a single LED in pulse mode. I tried various colors and styles of LEDs, and the results were mixed; sometimes the brightness change was dramatic, and sometimes it was mainly a color shift. High brightness LEDs with a narrow field of view responded very well to the pulsed mode operation, whereas low power LEDs with a diffused lens did not. The good news is that infrared LEDs are similar in characteristics to high power LEDs with a narrow field of view, so they should be the type to respond well to the pulse mode operation. Also, since 880 nanometer infrared radiation is slightly better than 940 nanometer radiation for night vision, the slight change in the spectrum will work in our favor here (if there is any).

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