Actually they should be connected in parallel. Because tungsten resistance increases with temperature, if one bulb starts out with a slightly higher resistance, it will get hotter faster and you will end up with inconsistent lighting or damaging that one bulbs (if not designed for operating at 120V nominal. 6 ideal bulbs in series would operate at 20V which would necessitate lower resistance and would explode at 120v). The higher temp and resistance would cause it to generate a higher than normal voltage drop/current/power, likely much more than the designed power, and the other bulbs may be much dimmer in comparison.
Also if one bulb drops out / blows it will take out all 6. Either way the power (150W) would be the same.
Actually they should be connected in parallel. Because tungsten resistance increases with temperature, if one bulb starts out with a slightly higher resistance, it will get hotter faster and you will end up with inconsistent lighting or damaging that one bulbs (if not designed for operating at 120V nominal. 6 ideal bulbs in series would operate at 20V which would necessitate lower resistance and would explode at 120v). The higher temp and resistance would cause it to generate a higher than normal voltage drop/current/power, likely much more than the designed power, and the other bulbs may be much dimmer in comparison.
Also if one bulb drops out / blows it will take out all 6. Either way the power (150W) would be the same.