One bulb to light them...

“Use only a single bulb in a multi-socket fixture. Be sure to check the maximum wattage the fixture allows

https://www.powerhousetv.com/EnergyEfficientLiving/EnergySavingTips/101WaysToSaveEnergy?utm_source=WS&utm_campaign=Energy-EfficientLiving/Energy-savingsTips/027471