There are several troubleshooting steps you can take:1. Check the bulb - Sometimes a poor contact between the light base and the fixture can cause issues with the flow of an electric current. Make sure your bulb is firmly tightened in the light socket. Also, ensure the screw base of your light fixture is not corroded.You can also check the bulb in another, compatible light fixture that you know is working.2. Check the fixture - Remove the bulb and replace it with a bulb that you know works in a similar fixture. Screw in the 2nd light bulb and turn on the light. If the 2nd light does not work, continue to Step #3 and #4.If the 2nd bulb works (and you are not using a dimmer or timer), then it is possible the 1st bulb is somehow at fault. Please review the rest of the troubleshooting steps before contacting customer service. We stand by our products and provide an industry leading warranty, so you don’t have to worry about malfunctions. Please contact our Customer Service Specialists for additional help, if these steps do not fix the issue.3. If you are using a timer using add-ons (such as timers, photo controls or occupancy sensors) - Sunco LED bulbs and retrofit downlights are not designed to be compatible with photo controls, occupancy sensors or timing devices. Please remove the timer or use the D2D bulb in another light fixture without a timer.4. Check dimmer compatibility - There are multiple types of dimmers available on the market that will function with dimmable Sunco LEDs. First, confirm your bulb is dimmable by viewing the tech specs on our Manuals & Documentation page. You can also view our dimmer compatibility list for each dimmable product. Drill down to find the product, then click on the green button to view the dimmer list.NOTE: Smart Bulbs are dimmable without a dimmer, when using the app paired with a compatible smart phone or tablet with WiFi. Dusk to Dawn and Motion Activated lights are not dimmable.