The base voltage of the transistor goes up to +6.5V. Its emitter goes up to 5.7v. Each red LED is about 1.8V so 2.1V is across the 100 ohms which is an LED current of 21mA.
Higher power LEDs have a higher voltage so the dimming will not be correct unless a higher battery voltage is used which will cause the transistor to get hot.
Use a 12V supply with 2.5V high power red LEDs.
The base of the transistor will go up to 8.7V. If the max LED current is 60mA then the transistor dissipates 198mW which is warm, not hot. The emitter voltage will go up to 7.9v and the current-limiting resistor will have 2.9V across it. For a max current of 60ma the resistor value should be 2.9V/60mA= 48.3 ohms. Use 51 ohms/one-quarter W.