Any physical element in a lighting system that manipulates light distribution. This includes lenses, reflectors, diffusers, and total internal reflection components. In luminaire design, the optic dictates the beam angle, field angle, and overall efficiency by capturing raw flux from the source and directing it exactly where it is needed.
The LED board is fine, but the optic got melted when the fixture overheated.
While optics is the science of light, in the shop, an optic is a physical piece of plastic or glass you hold in your hand.
Related terms
Lens
A shaped piece of transparent material designed to bend and focus light rays.
Beam angle
The angle across a light's beam at which intensity has fallen to 50 percent of its center value.
Luminaire
The whole light fixture as one product: light source, optics, housing, driver or ballast and power connection.