voltage divider to drive bulb
Just assume R2 \$\color{red}{\text{is}}\$ the 0.6 ohms of 21 bulbs in parallel and forget about adding a separate R2 resistor because that just eats power.

Or,

Put them in series parallel combinations. 3 series 3.8 volt bulbs is nearly 12 volts (11.4 volts) so you'd only need a small dropper resistor per series set of three and \$\color{red}{\text{not}}\$ waste a whole lot of power in R1.