The best way to light a makeup mirror is to mimic the lighting you will be seen in whether that's the sunshine in the day or indoor lighting at night. It's also important to position your lights so that they are not casting shadows across your face.
Overhead lighting is not recommended for applying makeup because of the shadows it will create across your face. Not only is this unflattering, it can also cause you to tilt your face in such a way that you are unable to apply your makeup with precision.
Instead, most makeup experts prefer a light source right in front of the face, preferably on both sides of the mirror. This ensures that both sides of the face are equally illuminated without glare. To transform a bathroom mirror into a makeup mirror, the optimum side lighting should have most of its luminosity at eye level and be placed around 18 inches from the center of the mirror.
The type of bulb in a makeup mirror is also important. Opt for either daylight spectrum or natural light bulbs, both of which replicate the glow of the sun. If possible, choose a lighting system that allows you to switch to a warmer glow in the evening. Avoid white fluorescent bulbs and yellow light, which can wash out the color of the face and make the skin appear sallow. Warm light at around 3,200 Kelvin is generally believed to be the optimum choice.