400nm

400 nanometers (nm) refers to a wavelength of light in the electromagnetic spectrum, about 0.4 micrometers. It corresponds to a photon frequency of roughly 7.5 × 10^14 hertz and a photon energy near 3.1 electron volts. This wavelength lies at the boundary between the visible spectrum and near-ultraviolet, with many people perceiving light at this wavelength as violet, though color perception can vary with context and individual sensitivity.

In standard terms, visible light is commonly taken to span roughly 380 to 740 nm, placing 400 nm at the violet edge. Because it is near the start of the ultraviolet region, light at 400 nm carries more energy than longer-wavelength visible light, which has implications for photochemical effects and material interactions.

Production and applications of light near 400 nm are widespread. Violet or near-UV light in the 400–405 nm range is produced by violet light-emitting diodes and diode lasers, and is widely used in consumer and scientific instrumentation. Notably, 405 nm lasers are employed inBlu-ray optical systems and in laboratory fluorescence excitation. In modern manufacturing and biomedicine, 405 nm light is used for photopolymerization in 3D printing resins, polymer curing, and certain fluorescence assays that rely on near-UV excitation. Safety considerations are important: near-UV and violet light can contribute to photochemical damage of eyes and skin with sufficient exposure, so appropriate eye protection and exposure controls are advised in high-intensity applications.

See also: visible spectrum, ultraviolet radiation, photon energy, laser diode.