Lighting 2 Quiz 1

Cornea

Clear outer parabolic portion of the eye. Provides most of the eye’s focusing power.

aqueous humor

Clear watery fluid between the cornea and the lens. Responsible for intraocular pressure and nourishes the lens and cornea.

Iris

Outer colored portion of the eye. Opens and closes depending on the amount of light trying to enter the eye.

Pupil

Hole formed by the opening of the iris. Pupil changes size depending on the light level to allow more or less light into the eye. Pupil acts as the aperture of the eye.

Lens

Sits beyond the pupil. Responsible of secondary focusing of light. Purpose is to focus a clear image onto the retina.

Ciliary muscles

responsible for flexing and changing the shape of the lens.

Accommodation

The adjustment of the lens via the ciliary muscles.

vitreous humor

thick clear gelatinous material that makes up 80% of the eye by volume. Responsible for maintaining the shape of the eye.

Sclera

White protective outer membrane of the eye. Responsible for maintaining the shape of the eye.

Retina

Light sensitive layers of nerve tissue at the back of the eye that receives images and sends them as electric signals through the optic nerve to the brain.

What are the three types of photoreceptors within the retina.

Rods, Cones, and ipRGCs

Rods and cones are responsible for …

image formation

ipRGCs stand for…

intrinsically photosensitive retinal ganglion cells

Fovea

Small portion of the retina where light is focused. High density of cones, NO RODS. The fovea is responsible for sharp central vision.

Fovea lives in a … field of view

2D

Extraocular muscles

set of 6 muscles that are responsible for smooth pursuit, saccades, and convergence.

Smooth pursuit

Eyes remain fixated on a moving object. (remaining on a smooth path)

Saccades

When scanning immediate surroundings, eyes make a saccadic movement, stopping several times and moving very quickly between each stop.

Convergence

Both eyes focus inward towards the nose to focus on close objects.

Adaption

A trio of processes by which the eye adjusts to a wide range of luminous conditions to preserve a steady visual experience.

Processes of Adaptation

1. Pupil Size

2. Opsins

3. Synaptic Interactions

Rods

1. only in periphery (not in the fovea)

2. Responsible for night vision

3. around 120 million

Peak sensitivity of Rods

507 nm

Cones

1. Located throughout the retina

2. most dense in the fovea

3. Responsible for daytime color vision

4. around 6 million

The three types of cones are …

1. short - peak at 448 nm

2. medium - peak at 541 nm

3. long - peak at 569 nm

Optic nerve

Carries signal from retina to the brain. Reason for the blind spot.

Retinal Cells consist of …

1. Photoreceptors

2. Horizontal Cells

3. Bipolar Cells

4. Amacrine Cells

5. Ganglion Cells

Photoreceptors

Convert light into an electrical signal

Horizontal cells

Work laterally and are inhibitory.

Bipolar Cells

Transmit signals between the photoreceptors and ganglion cells.

Amacrine Cells

Work laterally and are inhibitory. narrow field cells important for observing small dots moving a small distance.

Ganglion Cells

Receives signals from bipolar and amacrine cells. Transmits the final signal leaving the retina to the brain through the optic nerve fiber.

Some retinal ganglion cells arev…

directly light sensitive (intrinsically photosensitive retinal ganglion cells)

ipRGCs are responsible for our circadian rhythm? TRUE or FALSE

TRUE

ipRGCs peak wavelength is…

490 nm

Wavelength spectrum is (in nm) …

380 to 780

Photopic vision

1. Daytime vision

2. Cones fully engaged

3. Rods fully disengaged

Scotopic vision

1. Night-time vision

2. Cones fully disengaged

3. Rods fully engaged

Mesopic vision

1. Cones partially engaged

2. Rods partially engaged

Photopic Visual efficiency function: V(lamda)

Demonstrates the relative visual response (brightness match) at each wavelength (lamda) under photopic conditions.

Most used function in architectural lighting.

Under photopic conditions, the peak wavelength is …

555 nm

1 W of monochromatic light at 555 nm has an efficacy of …

683 lm/watt

Scotopic visual Efficiency Function: V’(lamda)

Determines the relative visual response (brightness match) at each wavelength under scotopic conditions.

Under scotopic conditions, the peak wavelength is …

507 nm

1 W of monochromatic light at 507 nm has a scotopic efficacy of …

1700 lm/watt

Purkinje Shift

Photopic to Scotopic shift

The tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.

Visual Deficiency: Presbyopia

With age, the lens of the eye becomes less flexible and less able to focus light onto the retina. This decreases accommodation ability.

Visual Deficiency: Macular Degeneration

Cell death at the retina. Causes blurred vision, difficulty seeing in low light, etc.

Visual Deficiency: Sighted-ness

Shape of the eye changes, causing Myopia (near-sightedness) or Hyperopia (far-sightedness).

Myopia

Near-sightedness

Hyperopia

Far-sightedness

Visual Deficiency: Astigmatism

A visual defect caused by unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.

Visual Deficiency: Keratoconus

Thinning of the cornea causing a cone-shaped bulge to form.

Visual Deficiency: Glaucoma

Eye condition that damages the optic nerve. Can lead to vision loss or blindness.

Visual Deficiency: Color Blindness

Marked by the deficiency of 1 or more of the cone photoreceptors.

MONOchromacy

Total color blindness, lacking at least two (possible three) of the cone photoreceptors. Sees only in black and white.

DIchromacy

1 or the cone photoreceptors is missing, and color is reduced to two dimensions.

Protanopia

Dichromacy - missing the long wavelength photoreceptor

Deuteranopia

Dichromacy - missing the medium wavelength photoreceptor

Tritanopia

Dichromacy - missing the short wavelength photoreceptor

4 factors affecting visual performance include …

1. Contrast

2. Size

3. Adaption luminance

4. Viewing time

Sensitivity of the eye is NOT equal across wavelengths. TRUE or FALSE

TRUE

Nutting determined in 1907 that …

Sensitivity of the eye is NOT equal across wavelengths.

Herbert Eugene Ives decided …

That there needs to be a standard field size used (standardize visual field for same ratio of rods and cones)

Produced his own luminosity function of the human eye.

v(lamda) is the only international unit based on …

Human perception (not physical)

Monochromatic light

Light of a single wavelength

V(lamda) is a…

standardized visual efficiency function. It is a standard observer that was determined as an average across multiple subjects and different experimental protocols. Represents an average observer.

Benefit of v(lamda)

accurate and reproducible quantifications of light sources.

Cons of v(lamda)

1. Small field of view

2. field luminance not representative of building interiors

3. Additivity assumption (fails for real world brightness matching)

4. Experimental methods

Visual efficiency function V() changes due to …

1. Field size (field of view)

2. adaptation state (more light v(), less light V’())

Photopic Luminous Flux is the … fundamental quantity of light.

First

Photopic Luminous Flux

Time rate of flow of radiant energy, evaluated in terms of a standardized visual response.

Symbol: Phi

Unit: Lumen (lm)

Equation: integral formula

Luminous Flux is measured in a device called …

integrating sphere

Luminous flux typically includes all light emitted by a luminaire. TRUE or FALSE

TRUE

Luminous Intensity

The luminous flux per unit solid angle in a specific direction.

Symbol: I

Unit: Candela (cd) or (lumen/steradian)

Equation: Phi / steradian

A full circle has … steradians

4 Pi

Luminous Intensity is measured with a …

Goniophotometer

Illuminance

The amount of luminous flux falling on a surface per unit area.

Symbol: E

Unit: footcandles or lux

Equation: I / D²

• D = distance

1 footcandle (lm/ft²) is equal to … lux (lm/m²)?

10.76

Illuminance: Inverse Square Law

The illuminance on any surface varies as the cosine of the angle of incidence varies.

Equation: E= (I*cos(theta)) / D²

• Theta = angle of incidence

• D=Distance

Angle of incidence

Angle between the normal to the surface and the direction of the incident light.

Illuminance is measured with an …

Illuminance meter

Exitance

The amount of luminous flux leaving a surface at a point.

Symbol: M

Unit: Lumens / area

Equation: M = E * p

Specular

The angle between the reflected ray and the normal to the surface will be equal.

• mirror is a specular material

Diffuse

reflect the optical radiation at many angles.

• matte paint is a diffuse material

Lambertian

A Lambertian surface is perfectly diffuse. (equally bright in all directions - equal luminance from all viewing angles)

Lambert’s cosine law

Io = In cos (theta)

• only valid for Lambertian surfaces

• In = incident intensity

• theta = angle of incidence

Law of conservation

p + T + a = 1

Light can either be reflected (p), transmitted (T), or absorbed (a).

Luminance

Spatial flux density emitted by a surface. (Intensity of light emitted from a surface per unit area in a given direction.)

Symbol: L

Unit: cd / m²

Equation: L = I / Ap

• Ap = Area projected = Acos(theta)

• Theta = angle of incidence

• If L = I / A, then L = M / Pi

Overview of Photometric Quantities:

1. Luminous flux (Phi): light emitted by a light source in ALL directions.

2. Luminous Intensity (I): Light emitted by a light source in a particular direction.

3. Illuminance (E): Density of luminous flux ONTO a surface.

4. Exitance (M): Density of luminous flux LEAVING a surface.

5. Luminance (L): Amount of light leaving a surface in a particular direction.

• luminance is what the human eye sees

Efficacy of a source

Symbol: n

Unit: Lumens / Watt

Equation: n = Phi / P

• P = power