These were purchased to replace two 12v bayonet style bulbs in a fixture which is connected to a 24v transformer which is connected to a sunset/dawn sensor. Since they are 12 volts, they must be connected in series to reduce the input voltage to 12 volts. I used to use 12 volt incandescent bulbs wired in series the same way. Connecting two 12 volt lamps in series to a 24 volt transformer will reduce their lifespan. Light bulbs only last a few months, after which they have to be replaced. I installed them in August 2019 and the first wire series bulb just burned out. One more and go. I am very happy with their performance and would not resort to incandescent bulbs for this application. Highly recommended.
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