We recommend you use dimmers with our LED bulbs so allowing greater flexibility in differing daylight conditions. Your existing dimmer switches may not work properly with LED bulbs if they are leading edge dimmers and this may lead to a shortened bulb life, a lower light output and a buzzing sound. For an optimum performance, you must use trailing edge dimmers which have lower minimum loads and are designed to be used with LED bulbs. Dimmer switches have a minimum and maximum rating (Watts). LED loading cannot however be calculated in the same way as a traditional incandescent or halogen bulb. A good rule of thumb to apply (one that is used by most manufacturers) is to take the maximum rating of your selected dimmer switch and then divide it by 10. As an example – if you have a dimmer switch with a maximum rating of 200W (rule of thumb translates to 20W) so you can run five of our 4W Squirrel Cage dimmable LED light bulbs.