ipRGCs have peak sensitivity around which wavelength?

• A. 380 nm
• B. 420 nm
• C. 600 nm
• D. 480 nm

Answer: (D)

ipRGCs use melanopsin, which is most responsive to blue light in the mid-blue region. Their peak sensitivity is around 480 nm, so blue wavelengths around this point most effectively stimulate these cells to drive non‑visual responses like circadian signaling and pupil constriction. Wavelengths in the violet/near-UV range (about 380–420 nm) or in the red region (around 600 nm) are much less effective at activating ipRGCs, which is why 480 nm is the best answer.