Light- Properties Visible light comprises a small portion of the electromagnetic spectrum(光谱) Wavelength, A(nm) 10310 10 10 10 1010110310 Frequency. V(Hz) 10201018101610141012101010310510102 Gamm Ultra Radio radiation r X-ray violet Infrared Microwave wave 400 Visible spectrum 700 Hgh energy Low energy
Light – Properties ➢ Visible light comprises a small portion of the electromagnetic spectrum (光谱）
Light Properties Ultraviolet(uv light => 100-400 nm
Light Properties ➢ Ultraviolet (UV) light => 100 - 400 nm ➢ Photosynthetically Active Radiation (PAR) => 400 -- 700 nm • Violet => ~380 -- 455 nm • Blue => ~455– 500 nm • Green => ~500– 580 nm • Yellow => ~580– 595 nm • Orange => ~595– 620 nm • Red => ~620– 700 nm • Far Red => ~700– 775 nm ➢ Infrared => ~775– 100,000 nm
operties
Light Properties ➢ The particle aspect of light is described as a photon（光子）. • Each photon contains specific amount of energy called a quantum (量子) (plural quanta). • The energy of a photon (a quantum of light) is inversely proportional to its wavelength (λ). • Violet light (short λ) has almost twice the energy of red light (long λ)
Light -Properties Photons can be absorbed by atoms to excite electrons(e)into higher energy states, or dislodge e from atoms Photon ucleus Electron Ground state Excited state
3 Ways to Describe Light
3 Ways to Describe Light ➢ Light quantity-- how much? ➢ Light quality --composition with respect to wavelength. ➢ Timing - duration and periodicity