How do I find the right bulb size for my car?

The easiest way is to take out your old bulb and read the little code stamped on the metal base (such as "H7" or "12V 55W"). You can also open your car's owner handbook and check the bulb chart in the back.

Can I put LED bulbs into a car that has normal halogen lights?

Yes, as long as you buy the LED bulb with the exact same base code (for example, replacing an H11 halogen with an H11 LED). If your car shows an error light on the dash, you will simply need a CANbus-ready bulb.

Do I need to change both headlight bulbs at the same time?

Car light bulbs grow dimmer as they get older. If one bulb has burned out, the other side has been running for the exact same amount of time and will usually blow out soon after. Changing both together keeps both headlights equally bright and matching in color.

Why is it bad to touch the glass of a new bulb with bare hands?

Your skin has natural oils on it. If you touch the clean glass, that oil stays behind, heats up when the light turns on, and causes the glass to crack or burn out early. Always hold the bulb by its metal base, or wear clean gloves.