OHM's law is critical!
My first bit of advice would be to learn OHM's law. If you have a collector resistor of 100 ohm, and VC (voltage collector) is 7.2V, the most amount of current you'll squeeze out is: VC - (0.6 + 3.2) / 100 = ~34mA The 0.6 is the emitter drop on the transistor while the 3.2 is the drop on the LEDs.
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