Week 3B: Light and the eye

Three ways to look at light, three ways they ‘behave’

Rays, waves, particles

When light strikes the interface between two substances it can be

Reflected, refracted (transmission) or absorbed

Which action heats up the material the most: reflection, refraction (transmission) or absorbtion

Absorbtion

Law of Reflection

Angle of incidence = Angle of reflection

Three different types of reflection

Specular, diffuse, and spread.

Index of refraction

n = c / v

Snellius’ law

n sin(theta) = n’ sin (theta’)

Since the index of refraction of glass is higher than of air, the angle of refraction with the normal will be (…) (larger or smaller)

Smaller

Critical angle definition

Largest possible angle of incidence which still results in a refracted ray

Total internal reflection

Light cannot escape from a high density medium to a lower density medium

Critical angle degree

41.8

As a wave, light is characterized by:

wavelength, polarization (oscillation direction), intensity (amplitude of the wave)

Visible wavelengths for humans

400 till 700 (nanometer)

The spectral power distribution determines the (…) in the eye

colour

Black body radiation

The theoretical spectrum of emission from an idealized object that absorbs all incident radiation, emitting light across a range of wavelengths according to its temperature.

Black body radiation of a sufficiently high temperature is (…) (a colour)

White

Dispersion

The velocity of the wave depends on its wavelength

Diffraction and its result

Occures when a wave encountes an obstacle or a slit and causes interference

Interference with two slits: White stripes a result of (…) interference, and black stripes as a result of (…) interference

Constructive, destructive

What does the luminous efficiency curve show

The human eye is not equally sensitive to all wavelengths

Why do we need photometric units to describe light

Quantify light in ways that correlate with human vision ( allowing for accurate measurement and comparison of brightness and intensity. )

Light scattering is not absorption, it is (…) of light energy

Redistribution

Rayleigh scattering

Light interacts with particles smaller than its wavelength (leading to shorter wavelengths being scattered more than longer wavelengths)

1,2,3,4,5,6

Transmission, reflection, refraction, diffraction, absorption, scattering

Focal length f of a lens

Distance where rays from infinity converge to a point

Lens formula

1/object distance + 1/ image distance = 1/ focal length

Image size scale formula

- image distance/object distance*height object

Accomodation errors: Myopic

(Nearsighted) Distant object in front of retina

Accomodation error: Hyperopic

(Farsighted) Close object focused behind retina

The smallest object humans can still see formula

Tan (alpha(visual angle)) = s(linear size) / d (viewing distance)

Pupil size can vary between (…) and (…) mm in diameter

2, 8

How is light processed from eye to brain

Light is processed by retina, transferred via the visual pathway, processed in the visual cortex

1,2,3

Rod, cone, synaptic clefts

Sensitive at low light level (cones or rods)

Rods

Location of rods in your eyes

Parafovea

Location of cones in your eyes

Fovea

If you want to see a shooting star, what should be your visual strategy and why

Use your parafoveal vision because there are more rods

Stiles-Crawford effect

Light entering the eye near the center of the pupil appears brighter than light entering near the edge of the pupil — even if the light intensity is the same

Principle of univariance

Once a photon is absorbed, its effect is independent of wavelength

Cortical cells

Produce a high response for one orientation of the stimulus

Direction selectivity

Cortical cells that produce a high response for movement of the stimulus in one direction

Binocularity (Ocular dominance)

Some cortical cells respond equally well to stimulation of either eye, while other respond better to the signal of one eye

Inner (…) degrees of the retina takes up 50% of striate cortex

10

Difference between simple cells and complex cells for cortical cells & orientation tuning

Response depends on position of stimulus in the receptive fields vs. response does not depend on position of stimulus in the receptive field