What is the maximal absorption wavelength of chlorolabe?

• A. 530 nm
• B. 507 nm
• C. 426 nm
• D. 557 nm

Answer: (A)

Photoreceptors have pigments that respond best to specific wavelengths, giving each type of cone its characteristic color sensitivity. Chlorolabe is the pigment in the medium-wavelength (green-sensitive) cones, and its absorption is strongest in the green part of the spectrum. The peak absorption for chlorolabe sits around 530 nanometers, meaning photons near 530 nm are absorbed most efficiently and drive the strongest signal in these cones. Wavelengths a bit shorter or longer than this peak are absorbed less effectively, so they produce weaker responses in chlorolabe. For comparison, 507 nm is a blue-green but not the peak for chlorolabe, 426 nm lies in the blue/violet range more characteristic of cyanolabe, and 557 nm is closer to the L-cone peak around 560 nm. Hence, the maximal absorption wavelength for chlorolabe is about 530 nm.