Final answer:
Not all eyewear is safe for viewing the sun; specifically, photographic filters, smoked glass, conventional sunglasses, and homemade filters can allow harmful UV and infrared rays to pass through.
Step-by-step explanation:
Certain types of eyeglasses and sunglasses are not authorized for wear because they do not provide adequate protection against harmful rays of the sun and may cause permanent eye damage. Eyewear such as neutral density photographic filters, smoked glass, color film, and homemade filters that might seem to reduce the brightness.
Moreover, conventional sunglasses, unless explicitly designed for this purpose, are not suitable for directly viewing the sun because they cannot filter out the intense UV radiation that can lead to eye injuries. Safe options for protecting eyes from the sun include welders' goggles and specially designed eclipse glasses.
On another note, with the technological advancements in the optical field, lenses such as photochromic lenses have been developed. These lenses automatically darken under UV light from the sun to provide proper eye protection but return to a clear state indoors where UV light is absent.