The GOODSMANN 120 Watt transformer is a high-quality transformer built to withstand harsh outdoor elements. GOODSMANN transformers are able to reduce household electrical current output from 120 volts AC to a much safer 12 volts AC output, providing a safer more practical electrical current level. GOODSMANN transformers are easily installed making it perfect for do-it-yourself projects. GOODSMANN transformers come with a digital reading, automatic timer, and clock controls facilitating easy light automation. To decide which transformer best suits your needs use the below formula: Total watts of light bulb * number of light bulbs = Minimum transformer size. A standard bulb requires 30 watts of power. If you have 10 30-watt bulbs needing power, you will need at least a 300-watt transformer. 30-watt light bulb * 10 light bulbs = 300 minimum transformer size. We recommend purchasing at least 100 watts more than you calculated minimum transformer size. Once you discover how easy it is to install/complete lighting projects, you may wish to add additional lights using the same transformer. We have a wide selection of high-quality lighting products and it is amazing how much your outdoor space improves after installation. The GOODSMANN 120 watts transformer is designed primarily for Landscape lighting systems. Please browse through our lighting products and let us know if you need any help with selecting the right product for your needs.