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There is one important rule my dear friend. If one of your light bulbs has blown and you need to replace it, it may be a good idea to replace the corresponding bulb on the other side of the car as well. I came across an interesting site on google https://lowbeambulb.com/ which had all the information on low beam bulbs for cars. There is a wide variety of headlight bulb sizes and so it is important to choose the one that suits your car.