This lamp is 420mm and has a lamp wattage of 20 watts. However, it is important to ensure that the lamp is keyed to your system. This particular lamp part number applies to 3 different systems, however they are keyed differently depending on the system that they are designed for. Without the correct key in your lamp, the bulb will not work properly with your system. Take a look at the manufacturer on your lamp, and that will determine the correct 40040096 that you require.
If your system is a PURA, this is the lamp you require: Product ID # 386
If your system is a Genesis H2O, this is the lamp you require: Product ID # 385
If your system is a Genuine Aquaflow, this is the lamp you require: Product ID # 967
Simply enter the Product ID # into the search bar on our website, and it will take you to the correct product. Please do not hesitate to contact us for assistance or clarification.