Flashing LED with "bulb-effect"
Old LEBs (light emitting bulbs) heated up and emitted light fairly quickly, but took longer to cool down and stop emitting light.  You might try something around 10 ms time constant for on, and 50 ms for off.

It would be useful to have a voltage control the LED current.  This can be the base of a transistor with a resistor on its emitter and the LED on the collector.  That becomes a controlled current sink.

ut a cap on the base and a resistor across the cap.  Those two set the off time constant.  Drive the cap thru another resistor and diode or transistor.  The two resistors in parallel with the cap set the on time constant.