Instructions

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Caution: Never look directly into the LED when it is switched
on. The blue light especially can damage the retina. Because
the eye is less sensitive to blue light, the blue LED appears less
bright, but is still very dangerous to the eyes.
The colour-changing LED is operated in this experiment using
adjustable brightness. You can try another experiment. The
potentiometer is connected as a voltage divider, so that even
very small voltages from as low as 0 V can be set. If you turn
the knob slowly to the right and thus increase the voltage,
at first only the red LED will flash. Then the green will start
flashing. And only at significantly higher voltage, the blue LED
will start to flash. So, the voltage range of the LED colours
also apply here. The shorter the wavelength of the light, the
more voltage is required by the LED.