A question seen often on messages boards is “How do I prevent squinting when using a reflector? Squinting can be a big problem when taking natural light portraits outdoors. It is also a common complaint among amateur photographers using reflectors. To get a great expression from your portrait subject, you definitely want to do all you can to prevent squinting when using a reflector. When the sun is bright, generally it is best to have the sun behind your portrait subject. Because you are backlighting with strong sunlight, your subject’s face will then be shaded and under-exposed. In order to compensate, you will either need to use a flash or strobe, or a reflector.
Using a reflector to fill in the light is where photographers often struggle. The main cause of squinting when using a reflector is because the photographer is using the wrong reflector for that particular situation. Think about this: a silver reflector is almost like a mirror. If the direct sun was causing squinting, then reflecting the sun with a silver reflector will almost certainly also cause squinting. When reflecting bright light, it is better to use a white reflector.
Another way to help with squinting is the position of the reflector. This is discussed in more detail in this post.