what type of things do you build to trap or reflct light?

Question: what type of things do you build to trap or reflct light?
- Keywords:
  build,
  light
Asked by lauryn campbell to Simone on 8 Nov 2018.
- Simone answered on 8 Nov 2018:
  
  I build photonic crystals!
  
  They are materials made by tiny structures (small holes or pillars) periodically repeating on the surface.
  
  Light shining on these materials interacts a lot with the small structures and their periodicity lead light to create very controlled destructive and constructive interference, therefore being trapped in some regions and reflected in others.

Question: what type of things do you build to trap or reflct light?