One of the main decisions you need to make when ordering new spectacles is whether the lenses should be light-sensitive, or permanently clear.  Light-sensitive, or "photochromic" lenses are clear indoors and at night, but darken on exposure to sunlight.  The beauty of this is that your lenses adjust automatically to glare, providing a sunglass-like level of glare protection.  The best-known brand of photochromic lens technology is Transitions.

Photochromic lenses work by incorporating a chemical that activates on exposure to ultra-violet (UV) light.  This causes the lenses to darken in outdoor situations, even on overcast days.  They will not react to the light from fluorescent tubes, or from computer screens.  

Light-sensitive technology certainly makes your glasses more versatile.  Photochromic lenses block 100% of damaging UV rays, reduce glare pretty well, and are still transparent at night-time and in indoor situations.  They're a great all-round solution.

However, there are a few situations where photochromic lenses can be less than ideal.  These include:

  • Driving - windscreens block quite a lot of UV.  This means that your light-sensitive lenses will not be exposed to enough UV to darken fully when you're behind the wheel.  
  • Entering a dim room from a bright day - darkened photochromic lenses take a few minutes to fade back to clear.  It's not an instantaneous process.
  • Very high glare - for some people, the glare protection offered by photochromic lenses is not quite enough.

Overall, light-sensitive lenses are a great option.  They are the best way to get a lot of utility into a single pair of glasses.  However, in our opinion, they are best thought of as an improved version of clear lenses, rather than as a replacement for sunglasses. 

Our preferred recommendation at Cassidy Eyecare is for a general purpose pair in either clear or Transitions material, plus a pair of polarized prescription sunglasses for high-glare situations.