Many sources for monochromatic light can be used. Most lasers emit light of a very narrow bandwidth, and often provide a suitable light source. A helium–neon laser emits light at 632 nanometers (red), while a frequency doubled emits light at 532 nm (green). Various laser diodes and diode-pumped solid-state lasers emit light in red, yellow, green, blue or violet. Dye lasers can be tuned to emit nearly any color. However, lasers also experience a phenomenon called laser speckle, which shows up in the fringes.