LED I-V Curves

I thought it would be fun to do some quick-and-dirty measurements of the I-V characteristic of some LEDs I had laying around. I have no idea where they came from, but one is red and one is white.

Fun fact: white LEDs, which of course would require many junctions of varying bandgap to produce white light directly, are often implemented by coating a blue LED in a phosphor that downconverts some photons into the rest of the visible spectrum.

Ideally I would make something like the IV_Swinger to automate the measurements, but I just moved and I’m not sure where any of my microcontrollers are right now, so I did it old school and entered data by hand. The horror!

I connected my benchtop power supply to the LED in series with a 1k resistor. My multimeter tells me the 1k resistor is actually 993 ohms. I prefer measuring voltage to current where possible, so I opted to measure voltage across the resistor and use Ohm’s law to find the current through the LED.

Here are the results:

Red LED

In [1]: import matplotlib.pyplot as plt

In [2]: V = [1.3094, 1.5546, 1.6256, 1.639, 1.661, 1.676, 1.661, 1.68, 1.678, 1.69, 1.664, 1.692, 1.704, 1.688, 1.689, 1.709]

In [3]: I = [0.0, 0.0002, 0.0006, 0.0011, 0.0015, 0.002, 0.0022, 0.0027, 0.0031, 0.0036, 0.0041, 0.0046, 0.0055, 0.0061, 0.0067, 0.0073]

In [4]: plt.scatter(V, I)
Out[4]: <matplotlib.collections.PathCollection at 0x7f07534baf10>

In [5]: plt.xlabel('Voltage [V]')
Out[5]: Text(0.5, 0, 'Voltage [V]')

In [6]: plt.ylabel('Current [A]')
Out[6]: Text(0, 0.5, 'Current [A]')

In [7]: plt.title('Red LED')
Out[7]: Text(0.5, 1.0, 'Red LED')

In [8]: plt.show()
../_images/red-led-iv.png

White LED

In [9]: import matplotlib.pyplot as plt

In [10]: V = [2.359, 2.462, 2.53, 2.55, 2.635, 2.656, 2.676, 2.721, 2.731, 2.788, 2.805, 2.826, 2.867, 2.926, 2.94, 3.01]

In [11]: I = [0.0, 0.0, 0.0002, 0.0004, 0.0005, 0.001, 0.0015, 0.0022, 0.0029, 0.0036, 0.0048, 0.0061, 0.0073, 0.009, 0.011, 0.0141]

In [12]: plt.scatter(V, I)
Out[12]: <matplotlib.collections.PathCollection at 0x7f0753432670>

In [13]: plt.xlabel('Voltage [V]')
Out[13]: Text(0.5, 0, 'Voltage [V]')

In [14]: plt.ylabel('Current [A]')
Out[14]: Text(0, 0.5, 'Current [A]')

In [15]: plt.title('White LED')
Out[15]: Text(0.5, 1.0, 'White LED')

In [16]: plt.show()
../_images/white-led-iv.png