metamerism
(1)位变异构性
(2)条件等色，异谱同色

• ultraviolet telescope
• ultraviolet transition
• ultraviolet-transmitting filter
• ultraviolet transmitting filters
• ultraviolet vidicon
• ultraviolet wavelength
• ultrawide angle lens
• ultrawide angle photographic lens system
• umber
• umbra
• Umen-second
• umweganregung
• unaberrated system
• unactivated
• unactivated state
• unadjusted eye
• unaided eye
• unannealed
• unbacked film
• unbalance
• unbalanced sight
• unbiased
• unblanking
• unblemished surface
• unblocking