Transistor Collector Heats Up

I used power transistor to drive high power LED (used in streetlights)

I added resistor between the Transistor Collector and the LED to verify which part of the transistor causing too much heat, and found out that it is really on the collector part.

Originally, the LED is powered up by 42 DC Volts so I wanted to keep that source level.

I added Photoresistor to turn ON/OFF the LED

The problem is that the transistor heat much.

I also wanted to keep the luminous/power dissipated by the LED as much as possible.

UPDATE: I don't know the specs of the LED but I know the original power source of it: 24V - 40V; 0.45A - 0.8A; Maximum 42V

Answer

Oh, cripes. I'll add a BJT circuit that uses your existing TIP122. You don't specify the LDR, so I can't be sure I've got the hysteresis thresholds right. But I think these will do. I'm offering this because it's probably the "least change" to what you have now and it may work okay for you, assuming that I read you correctly when you updated your question. (But I lack enough information to know for sure.) I'm also assuming here that it is easier for you to grab a couple of jelly bean PNP BJTs than it is to grab a specific comparator IC.

Here it is, below. I'm going to stay with your drawing format which buses the power supply around. I don't like doing that, because it can distract from understanding the circuit. But I suspect it may communicate better in your case. So I'll stick with the format you are currently comfortable with.

^{simulate this circuit – Schematic created using CircuitLab}

I kept the \$200\:\textrm{k}\$ resistor near the LDR in your circuit, because I don't know what caused you to use that value. I felt safer keeping it in place, for now. You can adjust \$R_1\$ to change the light level threshold, a bit. Also, \$R_3\$ and \$R_5\$ have useful effects when you change them. But I think I really need to know what LDR you are using (datasheet?) before I can offer much better. At least, this provides a very versatile topology that can be adapted to your needs when more information is available. The basic idea is solid and it uses a key part that I know you already have (the TIP122) adding only a minimum number of cheap parts to get the rest done for you.