01 · BACK LIGHT
Light can reach the lens from behind as well as from the front
When the sun is behind or to the side, light can reach the inner surface of the sunglass lens.
Large lenses do not eliminate this if there is still open space between the frame and the face.
Light reaches sunglasses from behind and from the sides as well as from the front. When the sun is behind the wearer or a bright wall or vehicle is nearby, some of that light can strike the inner lens surface and be reflected back toward the eye. The result can be a visible image of the wearer own eye, face or surrounding bright objects.
02 · REFLECTION
The back surface can reflect some light toward the eye
Light reaching the inner lens surface can reflect back toward the wearer, making the eyes, face or bright surroundings appear faintly overlaid in the view.
This is best understood as a relationship between surface reflection and ambient light, not automatically as a lens defect.
Some light is reflected whenever it reaches an interface between materials of different refractive index, and the back surface of a sunglass lens is no exception. If rear incident light is reflected toward the pupil, it becomes an internal reflection. This can be a normal consequence of surface optics and ambient lighting rather than proof of a defective lens.
03 · DARK LENS
Back reflections can stand out more through a dark lens
A dark front tint greatly reduces light entering from ahead, while a bright reflection from behind can remain relatively noticeable.
That is why the inner reflection may be more distracting when the sun is behind you.
Dark lenses can make back-surface reflections more noticeable because the forward scene has already been strongly attenuated. A rear reflection of similar absolute strength can therefore have greater contrast against the darker view. Perception depends on the brightness ratio as well as the physical percentage reflected.
04 · AR
Sunglasses can use anti-reflective treatment on the back surface
A back-surface anti-reflective coating can reduce the amount of light reflected toward the wearer.
Some sunglass coating systems specifically emphasize low reflection on the concave, inner surface.
A back-surface anti-reflective coating can reduce the amount of light reflected from the inner surface toward the eye. It cannot reduce reflection to absolute zero, and it does not block light that enters directly around the lens from the side. Back-surface AR and frame coverage solve related but different problems.
05 · FRAME POSITION
The position of the frame relative to the face matters too
If the lens sits far from the face or the sides are very open, more ambient light can reach the back surface.
Check bridge height, face-form angle and lens-to-eye distance in addition to the coating.
Frame position changes how much rear and lateral light reaches the lens. A lens sitting far from the face or a frame with widely open sides can admit more stray light. Bridge height, face-form angle, vertex distance and overall frame width should therefore be considered along with back-surface coating when reflections are bothersome.
GLANOS LENS CHECK
If inside reflections are distracting
Notice whether strong light is coming from behind or the side.
Check whether anti-reflective treatment is present.
See whether the effect is stronger with darker lenses.
Make sure the frame is not sitting unnecessarily far from the face.
Adjust the wearing position to reduce unwanted ambient light where possible.
CAUTION
Back-surface AR cannot remove every form of glare
Reducing surface reflection and blocking strong ambient light entering directly from the side are different problems.
GLANOS EYEWEAR
Eyewear comfort has reasons.
Back reflection · AR · Sunglass coating · Ambient light · Fit