Dropping Resister formula

Correct. 

The power through each single-lamp 150 ohm resistor is Voltage x Current = 6V x 0.04 A = 0.24 Watts so use 1/2 Watt resistors which are of course very common and inexpensive.   

As you probably bought a bunch of 150 ohm resistors, put 3 of them in parallel (just like the 3 lamps in parallel) to "make" a 50 ohm, 1.5 Watt resistor.  That way you don't have to buy another resistor value with a 3x higher power rating.

i calculate you need a 50 ohm resister.

since you have 3 lamps at .040 amp the I =0.12 amps the E= 6 volt.

you divide 6 volts by 0.12 amps the 3 light currents are added together to = 0.12

. hence 6 divided by 0.12 amps = a 50 ohm resister!

OK

 hope this helps

Alan

Thanks very much for the quick replies.  You are right, Stan, I have a ton of 150 ohm resisters.  Will try your approach.