AREN 4830 Final Exam

Pendant Mount

suspended

An office is 15 ft by 15 ft with two luminaires, each of which has lamps producing 6000 lumens. If the CU value for the luminaires is 75% for the desktops, what is the estimated average illuminance on the desktops? (Rounded to the nearest whole number.)

40 fc

A light source has luminous intensity of 1000 candlepower at the center of its beam, and is mounted five feet above a table. The estimated illuminance on the table directly beneath the light source is:

40 lux

Wall grazer

A form of downlight where a luminaire set at the top of a wall that directs light down the face of the wall to illuminate it.

Wall washer

A form of downlight where a specially shaped reflector is used to create an asymmetric wash of light to illuminate a wall from top to bottom.

Candlepower

intensity of light, in a specific direction

Lumens

total light output

Luminous Power

total light power produced by a source (measured in lumens)

Provide the most important characteristic, consideration, or purpose for the following luminaire component: Reflectors

used to control the distribution of light through the specular, semi-specular, and/or diffuse reflection.

D=

Distance between source and point

Point Method

E=I/D2

Density of Light w/in a 3D angle

(lumens/steradian)

Light Loss Factors

-lamp lumen depreciation -ballast effect -ambient temperature -voltage -lamp burnouts

Accent Lights

1. Adjustable 2. Can act as a variety of lighting (downlight, etc.) 3. Mostly used in retail spaces because the flexibility allows lighting to change with the display

Track and Track Heads

1. Offers a flexible lighting system where lights can move, change, etc. (Not interchangeable between manufacturers) 2. Multiple power circuits in one track. 3. They serve multiple purposes: spotlights, wall washers, or decorative pendants.

Downlights

1. Produces direct downward source of lighting 2. can offer a variety of beam spreads 3. can be recessed, surface mounted, or pendant

Cove Lights

1. The light being produced is soft, ambient light and is not very useful for performance, tasks, etc. 2. The source of light is hidden by a shelf or ledge. 3. Light is reflected off of a surface and into a space to enhance overall brightness.

Suppose that you wanted to produce an illuminance of 200 footcandles on a statue, from a light source that is mounted 10 feet from the statue. What value of luminous intensity do you need coming from the light source in the direction of the statue?

20,000 cd

For the same luminaire used in #9 (6000 lumens output), the CU value for a 20' by 30' room is 0.80. How many luminaires would you need in this larger room to achieve an average illuminance of 64 fc?

8

If the cone of light produced by a luminaire is too narrow, what type of accessory would you specify? Explain. When would you use a cross baffle hood or barndoor?

A spread lens would be used to adjust the cone of light produced by a luminaire that is too narrow. A cross baffle hood or barn door would be used to hide the bright face of the luminaire and reduce glare.

Control zone

A system of one or more light sources being used for the same task and controlled by the same output.

Provide the most important characteristic, consideration, or purpose for the following luminaire component: Apertures

Apertures is the opening of a luminaire where light exits.

Awp

Area of the space in ft2

Ewp=LMSlum X Nlum X CUwp/Awp

Calculating Average Illuminance

Dimming systems in buildings provide convenience and aesthetics without changing the energy used by lighting.

False

Large Scale Controls

Capable of controlling multiple lights that perform more than one task, dim lights, turn lights off and on, raise or lower blinds, open or close curtains, audio/video system control, etc.

Centralized System

Central control center. One main housing with the dimming hardware that controls the lighting of multiple areas.

The reflectance values of room surfaces directly affect this value.

Coefficient of utilization

Dimming systems

Combine multiple dimmers that are configured to dim any load. Flexible, efficient, and clutter-free.

Passive infrared (PIR) occupancy sensors broadcast IR waves into a room.

False

The National Electrical Code (NEC) states that a lighting circuit can carry 100% of the rated power (Watts) of the luminaires.

False

The term "vacancy sensor" refers to an occupancy sensor that automatically turns lights on whenever someone enters a space.

False

A light source or luminaire typically has a single value representing its luminous intensity (candlepower).

False

How does the NEC ensure that various luminaires can work together on a single circuit, switch, or dimmer without overloading the circuit?

Finding the maximum amperage rating of a circuit or device and then finding the allowable wattage range with an equation where the amperage is multiplied by the voltage to then allow that number to be greater than or equal to the wattage range.

E=

Illuminance at point (footcandles or lux)

I=

Luminous intensity in the direction of the point

This calculation method accounts for direct light only.

Inverse square cosine law method

This calculation method is used to estimate the illuminance at a specific point.

Inverse square cosine law method

Calculating the illuminance at a point uses which of the following calculation methods?

Inverse square law method

The accumulation of dirt on a luminaire directly affects this value.

Light loss factors (LLF)

LMSlum

Lumen output of the luminaire used

Photometric

Of or relating to the branch of science that measures the intensity of light

Vacancy Sensor

Requires light to be manually turned on but will turn off when motion is no longer detected.

The height and proportions of a room are used to calculate this value.

Room cavity ratio (RCR)

Occupancy Sensor

automatically turns lights on and off when motion is or isn't detected

Ewp

average illuminance on workplane

Distributed System

Spread the dimming hardware over two or more locations. Opportunity to change the lighting from multiple places.

Ultrasonic occupancy sensors can detect smaller motions than PIR sensors.

True

Ultrasonic occupancy sensors detect motion by sensing a shift in frequency of the ultrasonic waves that reflect to the sensor.

True

What is the purpose of the flange on a luminaire?

The ring at the bottom of a reflector that hides the gap between the ceiling material and the reflector.

The textbook indicates that lighting designers are often concerned with wattage maximums when configuring lighting controls. Why is this important?

They determine how many luminaries can be connected to one switch or dimmer. This prevents a circuit overload.

A dual technology occupancy sensor combines both passive infrared and ultrasonic sensing technology.

True

A light source or luminaire typically has a single value representing its luminous power (lumens).

True

Lighting controls for daylighting can save energy in buildings by switching or dimming the electric lighting in areas where daylight is present.

True

Passive infrared (PIR) occupancy sensors require a direct line of sight to the motion being detected to work properly.

True

The term "control zone" refers to a group of luminaires that perform the same task and are controlled in unison.

True

Provide the most important characteristic, consideration, or purpose for the following luminaire component: louver/baffle

Used to block light at high angles to prevent glare.

Calculating the average illuminance in a room uses which of the following calculation methods?

Zonal cavity method

This calculation method accounts for both direct and inter-reflected light.

Zonal cavity method

This calculation method is used to estimate the average illuminance on a work plane.

Zonal cavity method

The factor that expresses the percentage of the total light source lumens that reach the defined work plane is the

coefficient of utilization

CUwp

coefficient of utilization (% of lumens onto workplane)

Illuminance

density of light onto a surface

Nlum

number of luminaries used

When a light source is pointed straight down, photometric measurement techniques consider the 0 degree angle to be in which direction?

straight down beneath the light source