ATTO dyes are characterized by strong absorption (high extinction coefficient), high fluorescence quantum yield, and high photo-stability. ATTO 633 has a maximum absorption at 629 nm and a maximum fluorescence at 657 nm. The fluorescence is excited most efficiently in the range 610 to 645 nm. This label is analogous to the well-known dyes Alexa 647, Alexa 633 and Cy5.