We haven't answered your question about resistor power rating in Watts yet.
The power rating is how much power, in Watts, that a resistor is able to take without damaging or destroying itself.
So first you work out the power dissipation that the resistor has in a particular place in a particular circuit.
Then you chose a resistor that has a higher power rating than the actual power the resistor will be taking in the circuit.
The power rating of a resistor has absolutely no effect on the electrical performance of a resistor (this is not quite true, but for this circuit it is).
Resistors come in standard power ratings, and the higher the power rating, the bigger the resistor normally is.
The normal resistor power ratings are: 0.125 Watts (eighth Watt), 0.250 Watts (quarter Watt), 0.5 Watts (half Watt) and 1 Watt (one Watt).
There are then the high power resistors of: 2 Watts, 3 Watts, 5 Watts, 10 Watts, 15 Watts .... 100Watts.
After that there are the very high power resistors up to any wattage you can think of. Incidentally, electrically, your kettle at home is nothing more than a 1000 Watt to 3000 Watt resistor.
As Les has deduced from your photograph one resistor in your constant current circuit is 15 000 Ohms and the other resistor is 120 Ohms
The 15000 Ohm resistor has 22.5V- 0.6V = 21.9V across it. The power in a resistor is V*V/R Watts so this resistor will be dissipating 21.9V * 21.9V/15000 Ohms in Watts. Thus the power dissipation in the 15000 Ohm resistor will be 0.032 Watts so any resistor will be OK from a power rating aspect.
The 120 Ohm resistor has 0.6V across it, so the power dissipated will be 0.6V*0.6V/120 Ohms in Watts. So the power dissipated by the 120 Ohm resistor will be 0.0003 Watts. Once again any resistor will be suitable, from a power rating aspect.
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