The human eye is a complex sensing device. The optic nerve needs a minimum of 2.10x10^-17J of energy to trigger a series of impulses that eventually reach the brain. How many photons of blue light (475nm) are needed? The human eye is a complex sensing device. The optic nerve needs a minimum of 2.10x10^-17J of energy to trigger a series of impulses that eventually reach the brain. How many photons of blue light (475nm) are needed?