Lighting Exam 2 study guide

In lighting, there are 5 metrics we use to describe lighting. Check all that apply.

### Exitance, flux, illuminance, luminance, and intensity

The density of light (or illuminance) on a given surface is a function of the ______ __and__ _______ of the light source from the surface.

Distance and angle

calculate the illuminance given the following room/luminaire parameters:

Space Dimensions:  Width = 20',  Length = 10',  Height = 8'

Luminaires: 6 downlights.  Each downlight has an output of 1200lumens that end up on the floor. 

E=36fc

select the best option listed below for a Light Loss Factor:

0\.85

calculate the illuminance given the following room/luminaire parameters:

Space Dimensions:  Width = 20',  Length = 10',  Height = 8'

Worksurface/Table Height = 3'

Luminaire: We have an accent light directly over the 3' high table.  The accent light has a center beam candle power of 1,500 candelas.  

E=60fc

Lumen

light output (total amount of light emitted from a light source)

Are more lumens brighter or dimmer than less lumens?

brighter

What does the wattage of a light source NOT tell you

how bright the light is

if lumens are the same…

…wattages will vary

If wattages are the same…

…lumens will vary

Footcandle (FC)

1 ______ is equal to the light produced by one candle at a distance of 1ft away

Luminous Flux

Luminance

Luminous intensity

Illuminance

Luminous Flux

time rate of flow of light

Luminous Intensity

amount of flux (lumens) contained within a solid angle

Illuminance

Flux (or lumens) falling on a surface per unit area

Exitance

luminous flux density leaving a surface

What are the 2 ways to reflect light?

Specular and Lambertian

Luminance

Amount of light leaving a surface in a given direction

Small sources produce a…

higher chance of glare

Bigger sources produce…

less glare

Inverse square law

Light is inversely proportional to the square of the distance from the source of light

What is the inverse square law used for?

To calculate the intensity of any distance

Cosine law for illuminance

The illumination of a surface is directly proportional to the cosine of the angle between the normal to the surface and the direction of incident light

How do you know to use the cosine law for illuminance formula?

Includes a degree for an angle

what is the lumen method calculation used for?

Calculate the light level in a room

==calculate the illuminance given the following room/luminaire parameters:== \n Space Dimensions: Width = 20', Length = 10', Height = 8’ \n Luminaires: 6 downlights. Each downlight has an output of 1200lumens that end up on the floor.

E=36FC

\
calculate the illuminance given the following room/luminaire parameters: \n Space Dimensions: Width = 20', Length = 10', Height = 8’ \n Target Illuminance = 50fc \n Luminaires: If there are 8 downlights – ==how many lumens per downlight?==

1,250 lm/downlight

==calculate the illuminance given the following room/luminaire parameters:== \n Space Dimensions: Width = 20', Length = 10', Height = 8’ \n Worksurface/Table Height = 3’ \n Luminaire: We have an accent light directly over the 3' high table. The accent light has a center beam candle \n power of 1,500 candelas.

E=60FC

\
Instead of solving for Illuminance ( E ), we know we need \n 100fc candles at the table so what is the intensity of light we would need to reach that footcandle. \n Space Dimensions: Width = 20', Length = 10', Height = 8’ \n Worksurface/Table Height = 3’ \n Target Illuminance = 100fc \n Luminaire: ==What is the required intensity of light?==

I=2500cd

\
In the image drawn, solve for E1 and E2 with the given parameters. \n Intensity of Light = 1500cd \n Cos() = cos(36.87) = 0.8 \n d1 = 4m \n d2 = 5m

E1=93.75 lux

E2=48 lux

What is considered the longest day of the year?

Summer solstice

Is the sun higher in the sky during the winter or the summer?

summer

Horizontal light shelves help to minimize direct light into the space and allow light to bounce further into the space. Which orientation do horizontal light shelves have the biggest benefit. 

South

Which of the following lighting metrics has the following definition: 'Flux (or Lumens) falling on a surface per unit area' and unit of measure is Footcandle(fc) or Lux(lx).

Illuminance

In studying the Inverse Square Law and Cosine Law we know from the light source, the illuminance is directly proportional to which two factors: 

Distance and angle

Which of the following lighting metrics is defined as :  'Amount of light leaving a surface in a given direction' or the perceived brightness. 

Luminance

If two light sources have the same lumen output, but the aperture of once source is 4" and the aperture of the other sources is 12". Which light source is going to have a higher chance of glare?

4” light source

If two different light sources(LED and incandescent) have the exact same lumen output (600lm), will they also use the same amount of wattage?

No, the wattages will be different

Benefits of daylight:

Sustainable, natural world connection (circadian rhythm), human benefits, etc.

Daylight hazards:

Heat gain, glare and contrast, damage to belongings, excessive window light, sunburn, etc

Light reflectance value

measures the amount of visible light that reflects from or absorbs into a painted surface

What are common luminaire symbols used for?

Identifying devices on a blueprint or wiring diagram layout