occupancy controls for lighting

Copyright © May 1997, Pacific Gas and Electric Company, all rights reserved. Revised 4/25/97

APPLICATION NOTEAn In-Depth Examination of an Energy

Efficiency Technology

OccupancyControls for

Lighting

Summary

Occupancy sensors-also called motion,or personnel sensors- react to variableslike heat and/or motion by turning lightson or off. They turn lights on when peo-ple are detected and, after an adjust-able predetermined period during whichpeople are not detected, turn them off.While they have potential to reducelighting energy consumption by 35 to 45percent or more, their savings and ap-plicability are very site specific.

The two primary types of occupancysensors are ultrasonic and passive in-frared. Passive infrared (PIR) sensorstypically detect occupants’ body heat.Triggering occurs when a change in in-frared levels is detected, such as whena warm object moves in or out of view ofone of the sensor’s “eyes”. Ultrasonic(US) sensors, by contrast, continuouslyemit and sample inaudible sound wavesand listen for a change in frequency ofthe reflected sound.

There are two basic mounting configu-rations for occupancy sensors. Ceiling-mounted sensors have an independentcontroller and/or power supply. Theymay be mounted high on a wall or in acorner, as well as on the ceiling. Wall-box sensors are primarily designed asretrofit replacements for common wallswitches. Both ceiling-mounted andwallbox sensors are available with ei-ther PIR or ultrasonic sensing units.

The performance and reliability of occu-pancy sensors are tied to a host of fac-tors, including the shape and size of aroom, the installer’s experience, andinteractions with ballasts, lamps and

Summary .............................................1

How This Technology SavesEnergy .................................................2

Occupancy Sensors - Types andPlacement............................................2

Applicability ........................................6

Field Observations to AssessFeasibility............................................8

Estimation of Energy Savings .........10

Cost and Service Life .......................11

Laws, Codes and Regulations.........12

Definition of Key Terms ...................13

References to More Information......13

Major Manufacturers ........................14

PG&E Energy Efficiency Information© “Occupancy Controls for Lighting”

other building components. Sensor in-stallations sometimes yield smaller thanexpected savings due to improper prod-uct selection or installation, or unantici-pated interactions with other buildingcomponents. Users can maximize theperformance and cost-effectiveness ofsensor installations by consideringthese issues.

How This TechnologySaves Energy

Occupancy sensors are switching de-vices that respond to the presence andabsence of people in their field of view.The system consists of a motion detec-tor, an electronic control unit and acontrollable switch (relay). The motiondetector senses motion and sends asignal to either close or open the relaythat controls power to the lights.

Most motion detectors use either ultra-sonic sound waves or infrared radiationtechnologies to sense motion. The con-trol unit collects information from thesensor and determines the occupancystatus of the space. In some cases, thecontrol unit can be calibrated to adjustthe sensitivity1 of the sensors to mo-tion. The controller also has a pro-grammable timing device that will turnoff the lights after the room is unoccu-pied for a specific period. Output fromthe control unit energizes or de-energizes a relay which opens or closesthe lighting circuit. A power supply is

1 Bold-Italic words are defined in the sectiontitled Definition of Key Terms

also an element of the system and isneeded to transform the line voltage forpowering the control unit’s circuit andfor sending output to the relay. The re-lationship between the power supply,relay, controller and motion detector isshown in Figure 1.

In most occupancy sensor systems, themotion detector and controller are inone package; the power supply and re-lay are another integral unit, sometimescalled a switch pack. In wallbox sen-sors, components are all in one com-pact package, designed to fit into anexisting switch box. The solid-stateswitches often used in these packagesare rated for relatively small loads.

Occupancy Sensors - Typesand Placement

Most occupancy sensors turn lights onor off by detecting heat or a shift in thefrequency of reflected ultrasonic soundwaves. Units that use audible sound ormicrowaves are less common. Each ofthese sensor types is discussed below.

Transformer(Power Supply)

Controller

LowVoltage

Relay

Luminaire

LineVoltage

Sensor

Figure 1: Occupancy Sensor ControlSystem (Source: CEC)


Passive Infrared (PIR) sensors

Passive infrared sensors are the mostcommon type. They “see” infrared heatenergy emitted by people. Triggeringoccurs when a change in infrared levelsis detected, such as when a warm ob-ject moves in or out of view of one of thesensor’s “eyes”. PIR sensors are pas-sive devices: they only detect radiation;they do not emit it. They are designed tobe maximally sensitive to objects thatemit heat energy at the wavelengthemitted by humans. They are strictlyline-of-sight devices. They cannot “see”around corners and a person will not bedetected if there is an obstruction, suchas a partition between the person andthe detector. PIR sensors are quite re-sistant to false triggering.

The detection pattern of PIR sensors isfan shaped, formed by the cones of vi-sion seen by each segment of the fac-eted lens. Since the sensor is most sen-sitive to motion that moves from onesensing cone to another, its sensitivitydecreases with distance as the gapsbetween sensing cones widen. MostPIR sensors are sensitive to handmovement up to about 10 feet, arm andupper torso movement up to 20 feet,and full-body movement up to about 40feet. The sensitivity range can vary sub-stantially, however, depending on prod-uct quality and electronic circuiting de-sign.

Ultrasonic (US) sensors

Ultrasonic sensors emit a high-frequency sound, above the human andanimal audibility ranges, and listen for achange in frequency of the reflectedsound. They are able to cover larger

volumes than PIR sensors and are no-ticeably more sensitive, but are alsomore prone to false triggering. Air mo-tion, due to a person passing an opendoorway, or the on-off cycling of anHVAC system, may trigger a poorly lo-cated or adjusted sensor.

The ultrasonic sound waves cover theaffected area in a continuous fashion—there are no blind spots or gaps in thecoverage pattern. For this reason ultra-sonic sensors are somewhat more sen-sitive to movement. For example, handmotion can be detected at about 25feet, arm and body torso out to 30 feetand full-body motion out to over 40 feet.In narrow spaces such as corridors andwarehouse aisles US sensors detectoccupants up to 100 feet. The sensitivityrange of different products will vary sig-nificantly.

Other sensor types

“Dual” technology (or hybrid) sensorsare offered by several manufacturers.They use both the infrared and ultra-sonic technologies simultaneously.These sensors combine the sensitivityof ultrasonics with the passive infraredunit’s resistance to false triggering.

Audible sound sensors listen for noisemade by people and machines, and as-sume that it is a result of occupant ac-tivity. They may react to nearby vibra-tion (such as a slammed door) or tostreet noise, and require relatively highsound levels.

Microwave sensors are similar to ultra-sonics in that they emit a signal—in thiscase a radio signal—and measure achange in frequency when that signal isreflected. At present, only one company


makes microwave sensors and very lit-tle data exist on field experience or in-stalled cost. They are used primarily inthe security and alarm industries.

Mounting Configurations

There are two basic mounting configu-rations for occupancy sensors. Ceiling-mounted sensors employ an independ-ent controller and/or power supply. Theymay be mounted high on a wall or in acorner, as well as on the ceiling. Wall-box sensors are primarily designed asretrofit replacements for common wallswitches. Both ceiling-mounted andwallbox occupancy sensors are avail-able with either PIR or ultrasonic sens-ing units. They can be combined tocover an oddly shaped or large room. Aperformance comparison of a variety ofsensor/mounting combinations is pro-vided in Table 1.

Ceiling-Mounted Sensors

Ceiling-mounted occupancy sensors arevery popular. The typical system con-sists of a motion detector/controller unitconnected to a "switchpack" housing,containing the power supply and relay.Low voltage wiring is all that is requiredfor communication between the switch-pack and the sensor.

Ceiling-mounted sensors are typicallyused in larger rooms because they cancover greater areas, and usually havethese characteristics:

MountingLocation

Sensor Technology

Angle of Coverage

Typical Effective Range1

Optimum Mounting

Height

Ceiling Ultrasonic 360º 500-2000 ft2 8-12’

Ceiling Passive Infrared 360º 300-1000 ft2 8-12’

Wall Switch Ultrasonic 180º 275-300 ft2 40-48”

Wall Switch Passive Infrared 170-180º 300-1000 ft2 48”

Corner Wide View Passive Infrared 110-120º To 40 feet 3-10’

Corner Narrow View Passive Infrared 12º To 130 feet 6-7’

Corridor Ultrasonic 360º To 100 feet 8-12’

High Mount Passive Infrared 12º To 100 feet To 30’

1 Sensitivity to minor motion may be substantially less than noted here, depending onenvironmental factors.

Table 1: Occupancy Sensor Performance Characteristics (Source: CEC)

Figure 2: Example Ceiling Sensor(Source: Manufacturer’s Literature)


• Most cost between $50 and $120,uninstalled, with relay and low-voltagepower supply.

• Ceiling-mounted ultrasonic occu-pancy sensors are available in cover-age patterns ranging from about 250 to2,000 square feet.

• Time delay and sensitivity controlsare mounted on the sensor, makingthem inaccessible to occupants.

• Installation of these units requiresopening the ceiling or wall, since theymust be hardwired to the electrical dis-tribution system. This results in a rela-tively high installation cost for retrofitapplications.

Wall-Mounted Sensors

Wallbox-mounted occupancy sensorunits were introduced for smaller officesand similar applications where thehigher cost ceiling-mounted units wereconsidered too expensive. These units

have all components in a single housingand can be easily wired into existingswitch boxes in the room.

Most have the following characteristics:

• They typically cost between $30 and$90, uninstalled.

• Their sensor pattern spreads primar-ily to the left and right (60° to 90° ineach direction) in the horizontal plane,but only minimally in the vertical plane.

• An off-auto switch is available to ei-ther manually shut off the lights when aspace is occupied, or allow the sensorto control lighting. Some also have amanual override to keep lights on whena room is empty, ensuring that light isavailable even if a sensor fails. A spe-cial key or tool is often required to acti-vate the manual override.

• Time-delay and sensitivity controlsare usually accessible without removingthe sensor from the switch box. Thetime delay before turning the lights off isadjustable in most wallbox units, typi-cally from 30 seconds to 15 minutes.Shorter and longer adjustment ranges offrom 10 seconds to 30 minutes areavailable.

Integration With DaylightingControl

Several manufacturers have recentlybegun to combine occupancy sensorswith photocell sensors for daylightingcontrol. Integrated devices are nowavailable for both ceiling-mounted andwallbox units. Integration of daylightingcontrols with occupancy sensors in thesame control spaces is, at best, of lim-

Figure 3: Example Wall Sensor(Source: Manufacturer's Literature)


ited utility. While there are some goodpotential applications, such as in ware-houses and malls, where simple con-trols will be effective, the utility of theseunits is severely limited in spaces thatcontain more precise and/or difficultvisual tasks. In addition, integrated day-lighting-occupant sensing schemes limitlighting control to on/off switching (asopposed to dimming). This can be an-noying to occupants. Dimming is mostoften the superior approach in daylight-ing applications.

Case Study: Large scale LightingControl in Manufacturing/OfficePark

The retrofit of occupancy sensor con-trols in a large manufacturing/officecomplex in California provides an ex-ample of how this lighting control tech-nology can be applied cost-effectively.More than 5000 occupancy sensorswere installed throughout the 27 build-ing, 3 million square foot campus facilitythat included manufacturing, engineer-ing and development offices and com-puter facilities. The building lighting waspreviously controlled manually throughcentral panels. The majority of thebuildings contained no light switches inthe individual offices. Energy monitoringof the lighting panels indicated that thelighting was on an average of 22 hoursper day. A new, more energy-efficientmethod was needed that would be flexi-ble, reliable and responsive to individualbehavior.

After a detailed study of three lightingcontrol alternatives, ultrasonic occu-pancy sensors were selected as themost appropriate and cost-effectivelighting control strategy. The new con-trol system was implemented in three

phases. In the test phase, seven unitswere installed in a standard office bayand their performance was monitored.On average the units saved 55 percentof pre-retrofit energy consumption. InPhase I of the project, 550 additionalunits were installed in a pilot program inoffices and conference rooms to furtherevaluate product performance, occupantsatisfaction and energy savings. PhaseI results showed high employee satis-faction and energy savings of about 50percent. In the final phase, 4600 unitswere installed at a cost of $850,000. Afollow-up analysis estimated a paybackfor the retrofit of 1.1 years.

Applicability

In the past, the biggest application pit-falls associated with occupancy sensorshave been problems caused either byusing inappropriate sensor sensitivitypatterns for the application at hand, orby the improper mounting location ofsensor units. Studies suggest that whenoccupants find lighting controls of anytype to be obtrusive, they will disablethem, thus negating any potential en-ergy savings. In most applications, sen-sor types, sensitivity patterns, mountingheights, and locations should be basedon the recommendations of the manu-facturer. Typical applications of occu-pancy sensors are shown in Table 2.

Applicability to Lamp-BallastSystems

Occupancy sensors are appropriate forcontrolling both incandescent and rapid-start fluorescent lamps. With theselamps, reduced lamp life due to frequentswitching is not a significant problem.


Occupancy sensors are less compatiblewith both preheat and instant-start fluo-rescent lamp-ballast systems, such ascompact fluorescent lamps, F96T12slimline systems, and F32T8 lamps op-erated in instant-start mode. Lamp life inthese lamps is more sensitive to fre-quent switching applications than is thecase for rapid-start lamps. In applica-tions with occupancy sensors, it may bewise to consider the use of rapid-startelectronic ballasts for T-8 lamps ratherthan the more typical instant-start bal-lasts.

Some wallbox sensor circuitry designsmay not be completely compatible withcertain electronic ballasts, when com-bined with solid-state switching devices.Before using electronic ballasts in com-bination with occupancy sensors, the

designer is urged to check with the re-spective component manufacturers forcompatibility.

Occupancy sensors should not be usedwith high intensity discharge (HID)source lamps, except in a few specificcircumstances. Since HID lamps haveextended warm-up periods and cantake several minutes to restrike afterhaving been extinguished, occupancysensors are impractical for thesesources. A few manufacturers of HIDequipment, however, offer two-level(stepped dimming) HID systems specifi-cally designed to be used with occupantdetectors. In these applications, the low-light level is provided when no occu-pancy is detected. When the occupantdetector senses motion, it triggers thelighting system to go to the high level.

OCCUPANCY SENSOR APPLICATIONS

SensorType

Applications Notes

Ceiling Mount

Open Partitioned Areas,Small Open Offices,File Rooms,Reproduction Rooms,Conference Rooms,Restrooms, Garages

Provides for 360° coverage;derate range by 50% if par-titions >48” are in place

Corner MountWide View

Large Office Spaces,Conference Rooms Mount high on wall

Wall SwitchPrivate Offices, CopyRooms,Residences, Closets

Especially suitable forretrofits. Not recommendedfor areas with obstructions.

Narrow ViewHallways, corridors,aisle ways

Work best if mounted oncenters with range control

High MountNarrow View

Warehouse aisle waysMust be set back from aisleso that they do not detectmotion in cross aisles

Table 2: Typical Occupancy Sensor Applications (Source: CEC)


Since the lamps are already warm,these systems can go to full light outputvery quickly, provided they start from alow-light level rather than from off.These two-level systems may be quiteuseful in warehouse aisles, prisons,gymnasiums, and other interior applica-tions where a low light level is desirableeven when the space remains unoccu-pied.

Field Observations toAssess Feasibility

This section discusses considerationsthat should be made in selecting andplacing occupancy sensors. The dis-cussion also includes actions that canbe taken to ensure that energy savingsachieved by occupancy sensors will besustained.

Basic Sensor Specification

A good sensor should have:

• An easily accessible, well-labeled,and adjustable "on" period betweensensed motions, preferably as short as15 seconds (or shorter with a "cheaterkey", for easy testing) and as long as 20minutes to ensure no false "offs" (suchas when a computer operator's back isto the sensor).

• An easily accessible, well-labeled,and adjustable sensitivity control thatprovides a wide range of sensitivity toaccount for sensor placement and pos-sible sources of false triggering (e.g., anearby air diffuser).

• Protection from false triggering dueto radio frequency interference, or poorgrounding.

• Circuitry that fails in the "on" positionso failure will avoid a hazardous condi-tion, and provide light while the failedsensor is being removed.

• No means to override it to "on" with-out a special key or tool.

• Clear and accurate diagrams show-ing shape and size of the sensed zones(and preferably a scaled template to al-low easy design layout with scaled floorplans) during full body motion, andseparately for hand/arm motion.

• Warranty covering replacement forat least three years after installation.

• No troublesome circuitry that limitsits applicability with other basic equip-ment, such as electronic ballasts. Suchassurances should be written into thewarranty.

• Sufficient sensitivity to be triggeredby a minor arm motion, such as reach-ing for a telephone, anywhere in theroom.

Related to Applicability

An important design consideration isdetermining the location of the detector.The following factors should be consid-ered in determining proper placement.

• The wallbox sensor is effectivelylimited to the position of the wall switch.One must be certain that there are noobstructions to limit its effectiveness.For the wallbox sensor to effectively


monitor a space with obstructions, itmay be easier to simply move the ob-structions rather than relocate the wall-box.

• Ceiling-mounted sensors should bemounted and aimed so that they acti-vate the lighting system as soon as aperson enters the space.

• Ceiling-mounted sensors may bemounted high on the wall as well as onthe ceiling. Mounting the system highhas two advantages: there are fewerpossibilities of obstructions, and thesystem will be near to the electrical dis-tribution system, thus easing installa-tion. Sensors should not be mounted inlocations, such as behind door swings,that may temporarily obstruct the detec-tion pattern. Neither should they bemounted so that they monitor areas out-side of the controlled space.

• To reduce the possibility of falsedetection, PIR sensors should bemounted no closer than four to six feetfrom HVAC vents or other heat sources.

• Ultrasonic sensors should not beplaced in close proximity to ventilationducts or open windows, where airmovement may cause false triggering.

• Environmental factors may limitsome applications. For example, tem-perature and/or high humidity can affectthe electronics of occupancy sensorsand reduce the detector's range of sen-sitivity. The monitoring range of ultra-sonic sensors, for instance, may be re-duced by temperatures under 0 °C (32°F).

• The rated range of ceiling-mountedsensors should be derated when theyare located in partitioned spaces, wherebarriers block the line of sight of the de-vices. For example, in spaces with par-titions of 48 inches or higher, the rangeof ceiling-mounted sensors will be re-duced by a minimum of 50 percent. Therated range of occupancy sensors willalso be reduced if the mounting heightis more than 13 feet.

• Occupancy sensors in all applica-tions should be tested for sensitivityboth initially and at intervals to ensurethat specified performance is met andhas not deteriorated or been compro-mised by environmental factors.

• Some buildings have area-widedimming systems that change the waveform of the power to the fixture circuits,resulting in an across-the-board powerreduction. Some sensors will work ac-ceptably well for a time and then fail be-cause their solid-state circuitry may bestressed by such a corrupted waveform.

Related to Energy Savings

Unlike an unseen electronic ballast that,once installed, will continue to drawfewer watts than its predecessor, sen-sors are quite visible and can be im-properly adjusted, stolen or vandalized,or fooled into perceiving human motionwhen a space is unoccupied. Manualoverride switches on some sensors cancause lights to remain on even whenspaces are unoccupied.

If occupants complain about sensor op-eration, a common response is to raisesensitivity to the maximum, which may


cause more frequent false triggering. Ifsuch action still fails to resolve theproblem, a manual switch may be re-installed, eliminating any savings.Proper installation design and follow-upadjustment are therefore essential partsof any sensor program. Building main-tenance personnel must be trained tokeep sensors operational, rather thandisconnecting them when problems oc-cur.

Estimation of EnergySavings

Energy savings for any particular occu-pancy sensor application will vary con-siderably depending on the size of thearea covered and the occupancy pat-tern. Savings claims made by manu-facturers range from 5 to 75 percent.Energy saving potential is highly de-pendent on baseline assumptions andoperation, but values of 35 to 45 per-cent are typical. Table 3 illustrates thetypical range of savings from sensor in-stallation in various types of spaces. Inall cases except open plan offices, thesavings often range by a factor of two orthree. This uncertainty makes it difficultto predict the performance and cost-effectiveness of any given installation.

In order to determine the cost-effectiveness of occupancy sensors, thedesigner should have some knowledgeof the expected occupancy patterns ofthe spaces under consideration and ofthe amount of the power to be con-trolled. It may not be cost-effective, forinstance, to use occupancy sensors inspaces where occupancy is constantand predictable, like a school class-room. A better choice in these cases

might be a time scheduling system or acountdown timer.

In retrofit applications, it is importantthat the designer know the layout of thewiring system in use. If the installationof occupancy sensors requires exten-sive rewiring, it may not be cost effec-tive.

Standard Savings Calculation

The following equations are recom-mended for use in estimating energysavings from occupancy sensors. Alter-native equations and further informationconcerning the estimation of energysavings can be found in the CEE pro-gram documentation filed with theCPUC.

ApplicationEnergy

Savings1

1-2 Person Offices 25 - 50%

Open Offices 20 - 25%

Rest Rooms 30 - 75%

Corridors 30 - 40%

Storage Areas 45 - 65%

Meeting Rooms 45 - 65%

Conference Rooms 45 - 65%

Warehouses 50 - 75%

1 Figures are based on Manufacturer's esti-

mates and represent maximum potential sav-

ings under optimum circumstances. Actual

savings may differ.

Table 3: Savings Potential withOccupancy Sensors (Source: CEC)


HCIFkw and HCIFheat are the heat/coolinteraction factors which account for re-duced electric air conditioning loadsand increased gas heating loads, re-spectively, due to the decreased lightingenergy. A table of these factors can befound in the program documentation.

Utilization_factor is the ratio of “on” fix-tures to the total installed fixtures. Thisfactor accounts for fixtures or lampswhich are not operational due to burnedout lamps, failed ballasts, or not beingturned on.

Cost and Service Life

Factors That Influence ServiceLife

Occupancy Sensors

It is difficult to adequately assess thelife span of occupancy sensor systems.Only one manufacturer has been mak-ing occupancy sensors for 15 years, soany manufacturer's claim of life spans inexcess of 15 years have yet to beproven empirically. Life cycle testingprocedures seem to suggest that a rea-

sonable life span estimate for most oc-cupancy sensors would be between 12and 15 years. Control units, on the otherhand, are estimated to have a life ex-pectancy of between 6 and 10 years.Generally, control unit failures arecaused by deterioration of the trans-former or relay within them. Deteriora-tion may be exacerbated by high hu-midity environments and/or temperatureextremes.

Effects on Lighting Systems

While lamp life in rapid-start lamps maybe significantly reduced by constantswitching, in most occupancy sensorapplications, average switching cycles(>15 minutes apart) are usually longenough to avoid problems.

Manufacturers of occupancy sensorshave argued that although frequentswitching may reduce lamp operatinglife, the overall service life of the lampwill be increased. This analysis is com-plex, as one must compare the lamp lifelost due to frequent switching and thelife lost due to deterioration of the tung-sten electrodes.

The use of certain wallbox sensors withcompact fluorescent lamps may causereduced lamp life, as some of these de-vices do not completely shut off the cur-rent to the lamp's ballast, causing thelamp to remain partially energized. Inmost cases, lamps controlled by wallboxsensors supplied with a separate neu-tral connection will not experience anyproblems. For other devices, the de-signer should examine the sensor'sspecifications (often printed right on thebox) for application limitations. Often,

( )

( )

kWsavings

# fixtures_controlled

(Watts / fixtureas - built

/ 103 )

Utilization_ factor

kWhsavings

kWsavings

hoursbase

hoursas - built

HCIFkW

thermtakeback

kWsavings

hoursbase

hoursas - built

=

×

×

=

× −

×

=

× −


the specifications will list minimumloading requirements or state that thedevice is intended for incandescent useonly. When in doubt, contact themanufacturer.

Factors That Influence First Cost

Decision-makers are faced with threetypes of application choices for a light-ing control system: retrofit, renovationand new construction. Table 4 showsthe five major cost factors that shouldbe considered for each type of applica-tion.

Typical Service Life

The PG&E CEE program assumptionfor both wall-mounted and ceiling-mounted occupancy sensors is 8 years.

Laws, Codes andRegulations

The National Energy Policy Act of 1992mandates ASHRAE 90.1, which en-courages sensors as its standard foracceptable lighting design in new facili-ties. ASHRAE 90.1 allows discounting

of installed lighting wattage in a new fa-cility to meet its power density limits, ifcontrolled by automatic devices such astimers and sensors. Under the NationalEnergy Policy Act, all state energycodes should include the procedures in90.1 or else demonstrate how an alter-native is comparable.

Under Section 119 of California's Title24, occupancy sensors must meet thefollowing additional requirements:

• Shall extinguish the lights no longerthan 30 minutes after last occupancy

• Shall have adjustable calibration forsensitivity to movement (non-PIR sen-sors)

• Shall be equipped with a visualand/or auditory status indicator

Occupancy sensors, like all other light-ing equipment, should be listed by Un-derwriters Laboratories (UL), and theyshould meet ANSI requirements. Ultra-sonic sensors must also meet the U.S.Food and Drug Administration's stan-dards for decibel levels and must be in-audible to human hearing.

ApplicationInitial Cost

Operating Cost

Installed Cost

Supply Circuit Layout

Building Design

Retrofit √√ √√ √√ √√ √√

Renovation √√ √√ √√

New Construction √√ √√

Table 4: Major Cost Factors for Lighting Control Applications(Reprinted with permission. Copyright 1989, Fairmont Press. All rights reserved)


(Note: Reference to Title 24 or anyother regulatory standard is intended forinformational purposes, and any suchreference is not intended to be authori-tative when applying any standard.)

Definition of Key Terms

• Coverage: Typically refers to thesquare footage around the sensor inwhich whole body motion is detected atmaximum sensitivity.

• Instant-On Circuitry: Will auto-matically switch on the lights, or be ca-pable of immediately sensing occu-pancy, when power is restored followingan interruption.

• Line-of-Sight: Indicates that a sen-sor cannot see around corners. Sincemost substances reflect (or otherwisefail to transmit) heat, any surfaceblocking the line-of-sight of a passiveinfrared (PIR) sensor will "blind" it to ac-tivity behind that surface—even if it ap-pears to be transparent. Ultrasonic (US)sensors are similarly limited, but cansense air moving around a barrier dueto motion behind it.

• Masking: A method for limiting theview of infrared sensors by attachingprecut opaque labels to portions of thesensor's lenses; doing so avoids detec-tion of movement outside the controlledarea (for example, near an open door-way).

• Sensitivity: Defines how well a typi-cal body motion is "seen" at a givendistance. Such motions are usually di-vided into two categories: whole body(such as a person walking through adoorway) and hand/arm, or limb, motion(such as someone reaching for aphone). There is no precise standard fora typical limb motion, so one sensormay be more sensitive than anotherwhen both claim to sense the same mo-tion at the same distance. Most sensorshave adjustable sensitivity.

• Time Delay or Cycle Time: The pe-riod between the last sensing of motionand shutoff of the lights. This period isadjustable on most sensors for periodsas short as 15 seconds (while testingsensitivity) or as long as 30 minutes.

References to MoreInformation

1. California Energy Commission,“Occupant Sensors,” Advanced LightingGuidelines, Second Edition, P400-93-014, March 1993.

2. E-Source, “Occupancy Sensors:Promise and Pitfalls,” Tech Update, TU-93-8, August 1993.

3. E-Source, “Lighting,” Technology At-las Series, Volume 1, 1994.

4. Thumann, Albert, “Lighting EfficiencyApplications,” Fairmont Press, 1989.


Major Manufacturers

The Watt Stopper2800 De La Cruz Blvd.Santa Clara, CA 95050Tel (800) 879-8585Fax (408) 988-5373

Novitas, Inc.1657 Euclid StreetSanta Monica, CA 90404Tel (800) 888-8006Fax (310)-452-7890

Unenco, Inc.2555 Nicholson StreetSan Leandro, CA 94577Tel (800) 227-0452Fax (415) 895-5753

Additional lists of occupancy sensormanufacturers can be found in Refer-ences 1,2 and 3. Information on thistechnology can also be found by con-tacting relevant trade organizations,such as the National Electrical Manu-facturer’s Association and the Illumi-nating Engineering Society of NorthAmerica.

occupancy controls for lighting

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