LED with constant current and 18V supply change

To check if the flow through the LED remains constant, we increase the supply voltage to 18V. The two voltages add up in a series circuit. We achieve this through a series connection of power-supply- and battery-brick. In this experiment it´s extremely important to check the correct polarity! The negative port of the battery-brick has to be connected to the positive port of the power-supply-brick. The light intensity of the yellow LED at the collector of the transistor remains nearly the same!