Lighting Exam 1

What is Light?

Visually evaluated radiant energy

What is the visible color spectrum?

380 - 780 nm

What is at under 380 nm?

Ultraviolet

What is at over 780 nm?

Infrared

What are the 5 fundamental lighting units?

Luminous flux, luminous intensity, illuminance, existence, luminance

Define luminous flux 

Time rate of flow of light, used to define the total amount of light output from a source (Lumens, Φ)

Define luminous intensity

Amount of flux contained within a solid angle, or amount of flux in a particular direction (Candela (cd), I)

Define illuminance

Incident flux density, or amount of flux falling on a surface from all directions per unit area (footcandle or lux, E)

Define exitance

Luminous flux density leaving a surface in all directions (lumen/ft² or lumen/m², M)

Define luminance

Density of light leaving a surface in a given direction (cd/m², L)

What its the equation for luminous flux

Integral from 380 nm to 780 nm of p(λ)*V(λ)dλ

What does the efficiency of a luminaire indicate?

Efficiency = Source Performance = total lumens emitted / total lumens produced

What is efficacy?

Lumens / watt

What is the formula for Luminous Intensity?

I = flux / steradian 

I = Φ / ω

Define steradian

Conic solid angle

Is luminous intensity independent of distance?

Yes, but highly dependent on geometry (polar plot)

What is the formula for illuminance?

E = flux / area

E = phi / A

What are the units for illuminance?

Footcandle or lux

What is the formula for exitance?

M = Leaving Flux / Area

M = Φ / A

What are the units for exitance?

Lumens / ft²

Lumens / m²

What is the formula for luminance?

L = Luminous Intensity / Projected Area

L = I / A_p = I / A cos(θ)

What are the units for luminance?

cd / m² or cd / ft²

What is the symbol for luminous flux?

Phi

What is the symbol for luminous intensity?

I

What is the symbol for illuminance?

E

What is the symbol of exitance?

M

What is the symbol for luminance?

L

How many lux are in a footcandle?

10.76 lux

What does a smaller circle on a luminance meter indicate?

It is measuring a smaller projected area, or a smaller steradian, so it is more precise.

What does the luminance meter measure?

The average luminous intensity over a projected area

What does the illuminance meter measure?

The amount of flux falling on the receptor head from all directions per unit area

What is the formula for the inverse square cosine law?

E = (I Cos(θ)) / D²

What is theta in with respect to the inverse square cosine law?

The angle between incoming light ray and perpendicular to surface

What is the inverse square law in for lighting?

E = I / D²

What is the Cosine Law for lighting?

E₂ = E₁Cos(θ)

What is the equation for reflectance?

ρ = M_reflected / E

What is the equation for transmittance?

Tau = M_transmitted / E

Define reflectance

Portion of incident light that is reflected

Define transmittance

Portion of incident light that is transmitted

What is diffuse reflectance?

Light reflecting off a rough surface that is scattered in many different directions

What is Lambertian reflectance?

Light reflecting off a perfectly diffuse surface reflected equally in all directions

What is specularity?

How light reflects off an object

What is a specular surface?

A surface in which the angle of incoming light is equal to the angle of the reflected light.

What is an example of high reflectance on a specular surface?

Whiteboard

What is an example of high reflectance on a diffuse surface?

White ceiling tile

What is an example of low reflectance on a specular surface?

Phone screen when off

What is an example of low reflectance on a diffuse surface?

Black felt

What is a formula that can be used to calculate luminance on a lambertian surface only?

L = M / Pi

What is an equation to describe lambertian reflectance?

I(θ) = I_Ncos(θ)

What is an equation to describe specular reflection?

θ_i = θ_r

What is the least accurate of the three ways to measure reflectance?

With an illuminance meter

ρ = M / E

How do you calculate reflectance with a luminance meter.

Take the luminance of a reflectance standard, then take the luminance of the surface without the standard. 

Use the equation ρ₁ / ρ₂ = L₁ / L₂

What is the most accurate way to measure reflectance?

Using a reflectance meter.

Does luminance change with distance?

No

On a specular surface, does luminance change with angle?

Yes

Does luminance change with angle on an almost perfectly diffuse/lambertian surface?

No

What are the three big aspects of lighting quality?

Human need, energy economics environment, and architecture

What are some examples of human need in lighting quality?

Visibility, task performance, visual comfort/glare, social/communication, health, safety, wellbeing, mood

What are some examples of economics, environment, and energy in lighting quality?

Initial cost, maintenance cost, operating/energy cost, environmental cost

What are some examples of architecture in quality lighting?

Form/style, codes, standards

What is quality lighting?

Lighting that is able to combine human need, environment energy economics, and architecture qualities

What are important aspects of task?

contrast, luminance, size, time

What are important aspects of lighting condition?

illuminance level, glare

What are important aspects of the observer?

condition of eye (age, eyesight), fatigue, state of adaptation

What is discomfort glare?

Sensation of pain or annoyance due to high luminance within the field of view

What is disability glare?

Impairment of visual task due to high luminance within the field of view

What are the four variables of direct glare?

Luminance of source (L_s), Luminance of background (L_B), size of source (S), and position of source off of line of sight (P)

What is glare proportional to?

Glare ∝ (L_s) (Size) / (L_B) (Position)

What is a common example of glare effecting someone?

The sun while driving

What is VCP?

Visual comfort probability.

Percentage of people who would find installation acceptable. 

Higher VCP → Lower Glare

What is UGR?

Unified glare rating.

Scale of 10 - 30

Higher number → more glare

How can we fix reflected glare?

Change the source - task - eye geometry.

Lower luminance of the source, raise the luminance of the background.

Change the specularity of the task.

What are some examples of initial cost?

Fixtures, installation, wiring controls, electrical distribution, design, HVAC, structural support, daylight systems

What are some examples of maintenance cost?

Cleaning, repairs, replacement of lamps, replacement of components

What are examples of operating costs?

Energy to fixtures, HVAC effects, daylight effects

What are some examples of environmental cost?

Production of lamps, drivers, luminaires, controls, transportation of equipment, light pollution, disposal (mercury), unethical sourcing of materials, energy production

What are some examples of architecture in lighting quality?

Form/style.

How do you want the space to look/feel

light illuminates architecture

What is code?

Something that must be followed by the law, such as NFPA egress lighting requirements

What are standards?

Recommended best practices, such as IES, dark sky ordinances

What are the anatomy of the eye?

Cornea, iris/pupil, lens, retina, humours

What are the anatomy of the retina?

rods, cones, optic nerve, IPRGC

What are the functions of the cornea?

Protects the eyeball because it has pain receptors.

Fixed lens, so it helps with focusing

What are the functions of the Iris/Pupil?

Controls the amount of radiation that gets in

What are the functions of the lens?

Changes shape via ciliary muscles to focus image onto retina.

What happens to the lens as we age?

It gets yellow, gets less pliable, and lower transmission

What are the three parts in the retina?

Rods, cones, IPRGC

What do the three parts of the retina have in common?

They are photosensitive cells that send signals to the brain

What is the fovea?

Central focal point of the retina

No rods at the fovea, all cones

Does the optic nerve have photocells?

No

What does IPRGC stand for and what do they effect?

Intrinsically photosensitive rental ganglion cells

What is the function of the humours?

Liquids to keep appropriate pressures within the eyeball

What is the most efficient color of light and what is the wavelength of it?

Green at 550 nm

What are rods good at?

Peripheral vision, movement, black/white, “scotopic” vision (low light levels)

What are cones good at?

Direct (central) vision (at the fovea), color, detail, “photopic” vision (normal light levels

How many types of cones are there?

three types (small, medium, large for wavelengths)

Draw a picture of luminous flux

phi

lumens

Draw a picture of luminous intensity

I

cd

Draw a picture of illuminance

E

fc or lux

Draw a picture of exitance

M

lumens/ft² or lumens/m²

Draw a picture of luminance

L

cd/m² or cd/ft²