This is a project of a fading or pulsing LED circuit using 555 timer IC. The circuit will fade in fade out or fade on fade off a LED. You can also connect more LEDs in the circuit. The heart of the circuit is a 555 timer IC that is connected as an astable multivibrator here. The fading of the LED
depends on the 100uF electrolytic capacitor.
The 1M variable resistor is used to adjust the delay in fading. The operating voltage of the circuit is 9 to 12 volt DC. In the place of LED you can use a white or blue LED or any 25mA LED. More LEDs can also be connected in parallel with a 390 ohms current limiting resistor with each LED. You can also try to connect three LEDs in a line with a 68 ohms resistor on 12 volt supply as shown in this circuit: Sensitive Sound Activated LED.