Parabolic mirror in a flashlight
A gallium nitride blue-emitting LED is covered with yellowish cerium-doped yttrium aluminum garnet crystals. When excited by blue light, the crystals emit yellow light that is mixed with the blue LED's and appears as white light to our eyes. The parabolic mirror is accurate in that all rays from the yellowish crystals are uniformly projected forward, and as seen in reverse by the camera.
Canon FD 100mm f/4 macro, Canon extension tube, taken at f/22
Parabolic mirror in a flashlight
A gallium nitride blue-emitting LED is covered with yellowish cerium-doped yttrium aluminum garnet crystals. When excited by blue light, the crystals emit yellow light that is mixed with the blue LED's and appears as white light to our eyes. The parabolic mirror is accurate in that all rays from the yellowish crystals are uniformly projected forward, and as seen in reverse by the camera.
Canon FD 100mm f/4 macro, Canon extension tube, taken at f/22