Lighting Exam 2

What are the 5 fundamental lighting units

Luminous flux (Φ), luminous intensity (I), illuminance (E), exitance (M), luminance (L)

Define luminous flux with unit, symbol, and definition

Luminous flux, lumen, (Φ), time rate of flow of light used to define the total amount of light output from a source

Define luminous intensity with unit, symbol, and definition

Luminous Intensity, cd, (I), amount of flux in a particular direction

Define illuminance with unit, symbol, and definition

Illuminance, fc or lux, E, incident flux density, or amount of flux falling on a surface from all directions

Define exitance with unit, symbol, and definition

Exitance, lumen/ft² or lumen/m², M, luminous flux density leaving a surface in all directions

Define luminance with unit, symbol, and definition

Luminance, cd/ft² or cd/m², L, density of light leaving a surface in a given direction

What is efficiency

efficiency = source performance = total lumens emitted / total lumens produced

What is efficacy

Efficacy = lumens / watt

What is the formula for luminous intensity

I = lumen / steradian = Φ / ω

What is the formula for illuminance

E = flux / area = lumens / ft² or lumens / m² = Φ / A

What is the formula for exitance

M = leaving Φ / area = lumen / ft² or lumen / m²

What is the formula for luminance

L = luminous intensity / projected area = I / Ap = I / Acos(θ)

What is the inverse square cosine law

E = Icos(θ) / D²

What is theta in the inverse square cosine law

The angle between incoming light ray and perpendicular to the surface

What are the 8 qualities of light sources

Life, size, initial cost, efficacy, color (CCT and CRI), dimability, warmup and restrike, operating equipment required

What are advantages of incandescent lamps

Varies in size, very inexpensive, CRI = 100, dims beautifully, no warmup or restrike time, no equipment required, contains no mercury

What are disadvantages of incandescent lamps

Short life (2000 hrs), not very efficacious (16-20 LPW), not a wide CCT range (2200K-27000K)

How does an incandescent lamp produce light

Current through a metal filament which heats up. Some of the energy is emitted as light

What are advantages of fluorescent lamps

Very long life (20000hrs - 80000hrs), sizes small to large, inexpensive, good efficacy (90+ LPW), wide CCT range (3000K - 6000K), good CRI (80 - 90+), can dim (ballast), no warmup or restrike (compact have a little bit of warmup)

What are disadvantages of fluorescent lamps

They require a ballast, contain mercury, usually a pain to replace or maintain because they are generally in very difficult places.

What does a ballast do

Increase starting voltage and regulate current to keep the arc

What is the difference of high intensity discharge luminaires and fluorescent luminaires

The arc tubes are smaller, and internal pressures are different from fluorescent

What are advantages of metal halide lamps

Solid life (10 - 20k hrs), vary in size, good efficacy (75 - 90 LPW)

What are disadvantages of metal halide lamps

Expensive, doesn’t dim very well, 3-5 min warmup, 20 min restrike, ballast required, contains mercury, orientation must be considered (base up / base down), can have non quiescent failure, tendency to color shift over time

What are advantages of high pressure sodium lamps

solid life (10 - 30k hrs), vary in size, good efficacy (90-100 LPW), allegedly dim

What are the disadvantages of high pressure sodium lamps

Expensive, CRI = 20, CCT = 2100K, 1 min warmup and 4 min restrike, ballast required, contains mercury

What are advantages of low pressure sodium lamp

18k hrs of life, vary in size, very good efficacy (100+ LPW), no mercury

What are the disadvantages of low pressure sodium lamps

Expensive, can’t render color, low CCT (1700K), don’t think they dim, 15 min warmup and 4 min restrike. ballast required

How does an induction lamp produce light

Mercury vapor is excited by inducing a magnetic field

What are advantages of induction lamps

Very long life (100000 hrs), small - large sizes, inexpensive, good efficacy (90+ LPW), no warmup

What are disadvantages of induction lamps

Requires ignitor which only has a life of 50000 hrs, contain mercury

What is the main way LED’s produce white light

Blue LED with a yellow phosphor

What are the 2 other ways LED’s produce white light

UV LED with phosphor, or mix red green and blue to get white (RGB)

What are advantages of LED lamps

long life (L70 = 50000hrs), good efficacy (100+ LPW, but wide ranges), wide range of CCT, good dimability, no warmup or restrike, no mercury

What are disadvantages of LED

Small in size and require and array for enough light output, expensive but have now become the standard, driver required, must pull heat away from the LED using a heat sink, directional

What does a driver do in LED

Convert AC to DC, dimming, filter for bad power

What doe the chemicals in LED’s do

Chemicals used to determine wavelengths of photons emitted

What is daylight

Light from the sun and sky

What is daylighting

Delivery and distribution of light from sun and sky to the building interior to provide ambient and/or task lighting to meet the visual and biological needs of the occupants

Why do we use daylighting

It’s free, people enjoy the sun, helps with circadian rhythm, good color rendering, connection with the outdoors, or biophilia

Why do we not use daylighting

Glare, difficult to control/dim, the sun move, effects on HVAC

How do we get daylight into buildings

Solar path/angles, metrics, building orientation, daylight delivery systems

Describe the Omaha sun path

Most of the time the sun rises and sets in the southern sky dome, but in the summer months it rises and sets in the norther skydome

Describe altitude angle/solar elevation angle

angle from horizon to sun

Describe azimuth angle

The angle of the sun from due south. West of south is positive, east of south is negative

Describe the north facade of a buildings

High quality diffuse skylight for most of the year, low angle direct sun in the summer at early morning and early evening, rarely need glare mitigation (vertical shading device)

Describe the south facade of a building

Lot of direct sun, good for heat into space, bad for glare, must control glare

How should you mitigate glare in the south facade in the summer and winter

In the summer (high angle), use overhang or light shelf to block high angle direct sun while still allowing the view

In the winter (low angle), use blinds to block low angle, but lose view

Describe the east facade of a building

Low angle direct sun in the morning, diffuse skylight in afternoon/evening

How should you mitigate glare on the east facade of a building

Vertical shades

Describe the west facade of a building

Low angle direct sun in evening, diffuse skylight in morning/afternoon

How should you mitigate glare on the west facade of a building

Vertical shades

Why is measured illuminance less than calculated illuminance

Surfaces absorb light (CU), E = Φ/A gives an area, some lamp lumens don’t get out of the luminaire (CU), lumen loss over time (LLF), room geometry (CU)

What is zonal cavity

Zonal cavity is flux/area, factoring in CU and LLF

Ewp = (flux)(CU)(LLF) / A

What is the workplane

Imaginary horizontal plane at the height at which the task will be performed

What is coefficient of utilization

Percentage of lamp lumens that reach the workplane, both directly and through interreflections

What are some reasons why some lumens wouldn’t reach the workplane

light absorbed by surfaces, some light doesn’t get out of the luminaire

What are the 2 assumptions of zonal cavity

Luminaires are spaced uniformly in the space, empty rooms with perfectly diffuse surfaces

What is CU affected by

room surface reflectance, room shape, efficiency of luminaire

Describe how room surface reflectance affects CU

The higher the reflectance, the higher the CU, and vice versa

Describe how room shape affects CU

The ratio of vertical to horizontal surface area. Higher ratio → lower CU. Wider rooms have higher CU that tall rooms.

Describe how efficiency of luminaire affects CU

Efficiency ~ flux out of luminaire / flux generated by lamp. Higher efficiency → higher CU

Define RCR

RCR = 2.5 x (Vertical surface area of room cavity)/(Horizontal surface area of room cavity opening

What is the equation for RCR

RCR = 2.5 x (hrc)(perimeter of room)/Surface area

What are Light Loss Factors

Issues that affect light output (lab conditions vs real world conditions)

What are the 6 non recoverable LLFs

Luminaire ambient temperature, heat extraction thermal factor, voltage to luminaire, ballast factor, ballast lamp photometric factor, equipment operating factor

What are the 4 recoverable LLFs

Lamp lumen depreciation, luminaire dirt depreciation, room surface dirt depreciation, lamp burnout

How do you calculate ballast factor (BF)

BF = flux of actual ballast / flux of reference ballast

How do you calculate equipment operating factor (EOF)

EOF = flux at actual tilt / flux at intended tilt

How do you calculate lamp lumen depreciation (LLD)

LLD = mean flux / initial flux

How do you calculate luminaire dirt depreciation and room surface dirt depreciation

Graphs in IES handbook

How do you calculate lamp burnout (LB)

LB = number of lamps remaining operational / number of lamps total

What kind of lamps do luminaire ambient temperature affect

Fluorescent and LED

What kind of lamps do heat extraction thermal factor affect

Fluorescent

What kind of lamps does voltage to luminaire affect

Incandescent

What kind of lamps does equipment operating factor affect

Metal halide (sports lighting)

What is the formula for maintained illuminance on the workplane

Ewp = (number of fixtures)(lamps/fixture)(lumens/lamp)(CU)(LLF) / Area

How do you calculate spacing

spacing = sqrt(area/number of fixtures)

What is spacing/mounting height ratio

Maximum on center spacing for uniform illuminance / mounting height above workplane

How do you calculate average reflectance

average reflectance = P1A1 + P2A2 + P3A3 + … / A1 + A2 + A3 + …

How do you calculate reflectance of ceiling cavity

reflectance of ceiling cavity = 1 / 1+(As/Ao) + (1-average reflectance / average reflectance)

just write down

What is the 5 times rule

when you are going to photometer a fixture, you have to be at least 5 times the distance of the longest dimension of the fixture when measuring

Describe the SPD of incandescent 

Gradual growth from violet to red. More concentrated at the warmer colors. Merged together in the spectroscope

Describe the SPD of fluorescent

Good distribution overall. Peaks at violet, blue, and green. Falls off towards infrared

Describe the SPD of metal halide

Lot of spikes all throughout the SPD, making a lot of the colors very prominent. Merged vertical lines in the spectroscope

Describe the SPD of High pressure sodium

Prominent orange and green/yellow spikes in the SPD

Describe the SPD of Low pressure sodium

Very concentrated in orange

Describe the SPD of daylight

Very concentrated in pretty much every color. Prominent blue green and red

Describe the SPD of skylight

Thick faint lines merged together, less prominent colors without the sun

Describe elevation angle and azimuth angle when measuring illuminance of a source

The elevation angle the angle from NADIR to where you are measuring from, and the azimuth angle is the rotational angle from which you are measuring at the elevation angle. You are measuring intensity at those two angles

E = I(θ,φ)cosθ/D²

What is light

Visually evaluated radiant energy

What is color temperature

Absolute temperature (in kelvin) of a blackbody radiator whose chromaticity most closely resembles the color of the light source

What does a higher color temperature look like

More blue (cooler)

What does a lower color temperature look like

More red (warmer)

What is correlated color temperature

color temperature pf a source that falls off the blackbody locus

What is the blackbody locus

An ideal theoretical object that represents the color of an idealized blackbody radiator as temperature changes

What is a blackbody radiator

A theoretical object that perfectly absorbs all incoming electromagnetic radiation and emits radiation based solely on its temperature.

What is correlated color temperature (CCT)

Color temperature of a source that falls off the blackbody locus

What is color rendering

How well a source portrays different hues in the space

What is color rendering index (CRI)

One metric on a scale from 1 - 100 used to quantify how good a source renders color. 100 is based on a reference standard, and the reference standard is incandescent or daylight