OsramFCS 64640 HLX 150W 24V Tungsten Halogen Lamp

Q: Are the prongs flat or rounded

The pins of an FCS bulb, regardless of brand are round. An FCS bulb has what is called a G6.3 Base Type. The pins are 6.3mm apart from one another measured on center and the the pin diameter can vary slightly between .95mm and 1.05mm diameter and still be within spec. The pins are round.

Q: Does this work with outdoor landscape lighting which I think is 12v but I'm not sure.

For more than one reason, the answer is no. The FCS bulb is rated to operate at 24 Volts. If you have a 12 Volt system, meaning 12 volts at the socket, if you install the FCS bulb which is rated to operate at 24 volts, it will barely come on if at all. If it did come on, it would be very very dim. A second reason the FCS would not be a good choice for your application is the life hours. Even if the voltage was compatible, a FCS bulb is designed for use as a medical or optical device bulb and has an average rated life of only 50 hours. Even if the voltage were compatible, the FCS would be a very poor choice as it would burn out frequently. In contrast a typical bulb designed for landscape lighting would have a life hour rating of 2000 hours. To make a proper choice for a bulb for your landscape lights, first be certain of the voltage required at the socket, and second, know the maximum rated wattage recommended for the fixture and third, the base type required so that the bulb can be properly installed in the socket of the light.