+18 How To Determine Landscape Lighting Transformer Size Ideas. The final number 300w determines how large the transformer is that you`re going to need for your system. This will give you the recommended size of transformer that you should be using.
In this example, the total amount of power is over 200. Multiply the total by 1.25; Once you have that information, simply multiply the number of bulbs by the wattage.
