Wiki:
Light-activated resin:
“Light-activated resins are one-part translucent polymers that cure and quickly harden when exposed to specific light spectrums. The required wavelength for cure is specific to the resin chemistry.
The resin remains liquid (thick, like syrup or honey) under normal indoor lighting which allows the user to work with the material until curing is desired. After curing, light-activated resin is denser than air-cured resins due to its inherent chemistry and because no mixing is required that might introduce air bubbles.”
Exquisite Objects 