To be honest, i don't quite get what the schematic, and the voltage reference does, could you explain it to me?
Let's see if I get it (I'm not the best at electronics so I might be wrong...):
The transistor's resistance depends on the difference between base and emitter (Vbe). In this circuit the emitter isn't connected to ground so the voltage difference depends on the ratio of LED resistance to emitter resistor (they make a voltage divider). ie. Vbe isn't 1.4.
If I raise the supply voltage, the voltage at the transistor's emitter goes up, Vbe goes down. The transistor's resistance increases, the LED current goes down.
If I lower the supply voltage, the voltage at the transistor's emitter goes down, Vbe goes up. The transistor's resistance decreases, the LED current goes up.