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Construction Technology Update, 1997-12-01
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Office lighting investments : payoffs for people and the environment
Veitch, J. A.; Newsham, G. R.
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https://nrc-publications.canada.ca/eng/view/object/?id=41e44811-07e2-4db9-ae44-7dd731bdf8c9 https://publications-cnrc.canada.ca/fra/voir/objet/?id=41e44811-07e2-4db9-ae44-7dd731bdf8c9b y J.A . Ve itch a nd G.R. Ne w sha m
The lighting industry has been hampered by the lack of a w idely accepted
means of assessing lighting quality. This Update reports the first results
from a lighting quality research project conducted by NRC’s Institute for
Research in Construction.
C o n s t r u c t i o n T e c h n o l o g y U p d a t e N o . 1 0
Office con d ition s h ave ch an ged a great d eal in th e p ast th irty years. Flu orescen t ligh t-in g, th e m at-in stay of office ligh tt-in g st-in ce th e 1930s, m ostly con sisted of regu lar arrays of recessed lu m in aires w ith th e lam p s covered by p rism atic acrylic len ses. Th ese d irect ligh tin g system s p rovid ed brigh t w alls an d very brigh t h orizon tal su rfaces. Brigh t w orkin g su rfaces w ere believed to be im p ortan t to en su re task visibility, a con cern th at w as h igh ly ju stified : it w as n ot u n com m on for p eop le to sp en d h ou rs each
d ay read in g th ird -gen eration carbon cop ies, or fain t p en cil m arks on p ap er.
Tod ay, alm ost every office w orker sp en d s at least p art of th e d ay w orkin g on a com -p u ter, a fact th at h as -p rofou n d im -p lication s for office ligh tin g. In stead of read in g from a p iece of p ap er on a h orizon tal su rface, th ese em p loyees n ow read from a self-lu m i-n ou s, vertical glass screei-n . Th e lei-n sed lu m in aires th at p rovid ed good h orizon tal illu m in ation on d esks su d d en ly becam e sou rces of u n w an ted screen reflection s (see Figu re 1). Glare can red u ce a p erson ’s ability to read in form ation on a screen , w ith con sequ en ces ran gin g from in con ven ien t to d isastrou s, d ep en d in g on th e criticality of th e task an d th e exten t of th e p roblem . For exam p le, becau se stock trad ers n eed to be able to read , p recisely an d qu ickly, th e stock p rices on th eir m on itors, severe glare can lead to costly in accu racies in th e in for-m ation th ey su p p ly to th eir clien ts.
Conse nsus-Ba se d Light ing Re c om m e nda t ions
North Am erican ligh tin g recom m en d ation s for ligh tin g sp ecifiers an d d esign ers em erge from th e Illu m in atin g En gin eerin g Society of North Am erica (IESNA). Th e cu rren t stan d ard relevan t to office ligh tin g is IESNA RP-1 (1993), Am erican Nation al Stan d ard
Office Lighting Investments:
Payoffs for People and
the Environment
Figure 1.Luminaires behind the seated worker cause unwanted reflections on the computer screen.
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Practice for Office Ligh tin g. Table 1 p rovid es a su m m ary of th ese recom m en d ation s, w h ich are in ten d ed to p rovid e ad equ ate ligh t on th e d esk su rface to read d ocu m en ts, w h ile red u cin g th e d egree of glare on com -p u ter screen s. Lu m in an ce ratio lim its are in ten d ed to p reven t excessive con trasts betw een ligh t an d d ark.
Ligh tin g recom m en d ation s are n otoriou s for th eir w eak lin k to p u blish ed research , an d th e research literatu re itself is n otoriou s for its p oor qu ality. Th e recom m en d ation s are th e con sid ered op in ion of exp erien ced ligh tin g d esign ers an d illu m in atin g en gi-n eers, bu t th ey cagi-n gi-n ot assu re u s th at ligh t-in g d esign s th at m eet th ese recom m en d ation s w ill m eet th e n eed s of occu p an ts, con tribu t-in g to th eir task p erform an ce, com fort, h ealth , an d satisfaction .
Th e d evelop m en t an d ad op tion of en ergy cod es for bu ild in gs p oses an ad d ition al ch allen ge for office ligh tin g by p lacin g lim its on th e electric p ow er d evoted to ligh tin g. ASHRAE/ IESNA Stan d ard 90.1, En ergy efficien t d esign of n ew bu ild in gs ex cep t n ew low -rise resid en tial bu ild in gs, an d th e
Can ad ian Mod el N ation al En ergy Cod e for Bu ild in gs both lim it accep table ligh tin g p ow er d en sities for offices to ap p roxim ately 14 W/ m2. Th e n ew ly d evelop ed en ergy cod es an d stan d ard s h ave created ren ew ed fears th at red u ced en ergy for ligh tin g w ou ld lead to p oorer qu ality ligh tin g. Th is w as d em on strably th e case d u rin g th e 1970s en ergy crisis, w h en d elam p in g w as th e p re-d om in an t en ergy-savin g strategy. Are-d van ces in ligh tin g tech n ology h ave given rise to n ew altern atives for en ergy savin gs, bu t in th e absen ce of an y agreem en t on h ow to assess ligh tin g qu ality, th ere w as little con -fid en ce th at th ese n ew tech n ologies w ou ld p reven t a rep eat of earlier p roblem s.
I RC Light ing Qua lit y Re se a rc h
Th e Nation al Research Cou n cil of Can ad a’s In stitu te for Research in Con stru ction (IRC) resp on d ed to th is con cern w ith th e p roject “Exp erim en tal In vestigation s of Ligh tin g Qu ality, Preferen ces an d Con trol Effects on Task Perform an ce an d En ergy-Efficien cy,” w h ich began in October 1994. Its objec-tives are:
Table 1.Summary of recommendations from IESNA RP-1
Illuminance Max. ceiling Task: surround Task: w all Ceiling Other
on desk (lux) luminance luminance ratio luminance ratio max/min considerations (cd/m2) luminance ratio 300–500 (200–300 gen eral; 300–450 task) p referred : 850 @ 55-d eg an gle accep table: 850 @ 65-d eg an gle 3:1 10:1 or 1:10 40:1 m ax. ou tsid e field of view p referred : 4:1 accep table: 10:1 VCP* > 70 Reflectan ces an d fin ish es Main ten an ce
* visu al com fort p robability
Ba sic s of Fluore sc e nt Light ing
A flu orescen t ligh tin g system con sists of th ree p arts: th e lu m in aire, th e lam p s an d th e ballast. Lu m in aire is th e tech n ical term for an y ligh tin g fixtu re; it con tain s th e lam p s an d th e ballast, an d m igh t also in clu d e op tical d evices to d irect th e ligh t. Flu orescen t lam p s em it ligh t w h en th eir p h osp h or coatin g receives en ergy from gaseou s m ercu ry atom s excited by an electric arc. Th e ballast con trols th e electric arc across th e lam p s, p reven tin g th e voltage from in creasin g w ith d estru ctive effect.
Man y p eop le d islike an d d istru st flu orescen t ligh tin g. Am on g th e m ost com m on com p lain ts are “it flickers” an d “it h u m s.” Both are traceable to ballasts. Th e origin al ballasts for flu orescen t lam p s w ere coiled -core m agn etic ballasts, w h ich can p rod u ce an au d ible h u m [Rea, 1993], d ep en d in g on th eir con stru ction an d on th e lu m in aire. Magn etic ballasts, w h en op eratin g correctly, op erate flu orescen t lam p s at 120 Hz (2x th e 60 Hz AC cu rren t). Few p eop le can p erceive th is m od u lation in ligh t ou tp u t as flicker; h ow ever, as lam p s an d ballasts age, th e m od u lation rate can slow to th e p oin t w h ere flicker is p erceived . Th is can be a sou rce of an n oyan ce. Moreover, th ere is evid en ce th at th e n ervou s system can d etect lu m in ou s m od u lation u p to 147 Hz, even w h en th e observer d oes n ot rep ort seein g flicker.
Ad van ces in in tegrated circu itry h ave led to th e d evelop m en t of electron ic ballasts, w h ich op erate in th e frequ en cy ran ge 20 000–60 000 Hz. Th is frequ en cy is h igh en ou gh th at an y ballast n oise is in au d ible to h u m an s an d th e lu m in ou s m od u lation can n ot be d etected by th e n ervou s system . Fu n ction ally, electron ic ballasts are n oise- an d flicker-free. Th e h igh frequ en cy is d esign ed n ot to be so h igh as to cau se electrom agn etic in terferen ce. Electron ic ballasts h ave th e ad d ed ben efit of bein g m ore en ergy-efficien t th an m agn etic ballasts.
Tasks Performed
Tem p orary office w orkers (292 in total), recru ited from a local firm , p articip ated in th e exp erim en t. Each p erson w orked for on e d ay u n d er on e of th e n in e ligh tin g con d ition s; th ey w ere u n aw are th at th e exp erim en t con cern ed ligh tin g u n til th e en d of th e d ay. Ligh tin g con d ition s w ere ch an ged from d ay to d ay in a ran d om ord er to con trol for extran eou s variables. Du rin g th e d ay, th e w orkers p erform ed a variety of com p u ter-based an d p ap er-based tasks d esign ed to rep resen t m od ern office w ork, an d com p leted qu estion n aires to assess th eir satisfaction w ith an d im p ression s of ligh tin g qu ality, m ood , p h ysical com fort, an d social beh aviou rs. Th ey also d id visu al p erform an ce tests at the beginning and end of the day.
Results
Peop le w h o w orked u n d er ligh tin g system s w ith electron ic ballasts sh ow ed less visu al fatigu e at th e en d of th e d ay an d p erform ed better on read in g an d w ritin g tasks. Th ey also rated th e tasks as bein g less d ifficu lt th an d id p eop le w h o w orked u n d er ligh tin g system s lit w ith m agn etic ballasts. Figu re 4a sh ow s th at p eop le typ ed m ore d u rin g a w ritin g task w h en th e ligh tin g system u sed electron ic ballasts. Th is set of fin d in gs m irrors th e resu lts of oth er research at NRC an d elsew h ere, w h ich h as sh ow n th at h igh -frequ en cy electron ic ballasts im p rove visu al p erform an ce, im p rove eye m ovem en ts in read in g, an d red u ce th e in cid en ce of h ead ach e an d eyestrain .
Th e exp erim en t also sh ow ed th at ligh tin g system s d esign ed for com p u ter offices allow better p erform an ce of com p u ter-based tasks. Figu re 4b sh ow s th at ligh tin g sys-tem s w ith p arabolic lou vers w ere rated as bein g less glarin g th an th ose w ith p rism atic len ses, exactly as th ey are d esign ed to d o. • to ch aracterize office ligh tin g qu ality
u n d er d ifferen t ligh tin g d esign s, at ligh t-in g p ow er d en sities (LPD) typ ical of existin g con d ition s an d of cu rren t an d p rop osed en ergy cod es an d stan d ard s; • to relate th e task p erform an ce of office
w orkers to ligh tin g qu ality;
• to d eterm in e th e effect of an in d ivid u al’s con trol over office ligh tin g on h is/ h er satisfaction an d p erform an ce.
Resu lts from on e exp erim en t, ad d ressin g th e first tw o objectives, are p resen tly avail-able. An exp erim en t ad d ressin g th e th ird objective is u n d er w ay.
The Research Set-up
The first experiment took place in IRC’s Indoor En viron m en t Research Facility (see Figu re 2). Th e 83-m2 (880-ft2) sp ace is con figu red as a w in d ow less op en -p lan office area con tain in g six w orkstation s. Th ree ligh tin g d esign ers created n in e ligh tin g d esign s for th e sp ace. Th e d esign s com bin ed th ree levels of ligh tin g p ow er d en sity (LPD) an d th ree levels of Design ers’ Ligh tin g Qu ality (DLQ), w h ich th ey d efin ed by con sen su s, form in g a 3-by-3 m atrix of exp erim en tal con d ition s (see Figu re 3). All th e low DLQ con d ition s u sed recessed troffers w ith p rism atic len ses; m ed iu m DLQ con d ition s u sed recessed troffers w ith p arabolic lou vers; an d h igh DLQ con d ition s u sed in d irect or d irect/ in d irect fixtu res. Th e LPD levels w ere ap p roxim ately 9, 14 an d 25 W/ m2. In th e low LPD op tion s, th e am bien t ligh tin g system s w ere su p p lem en ted w ith task ligh t-in g. Th e m ed iu m an d low LPD con d ition s all u sed electron ic ballasts, w h ereas th e h igh LPD con d ition s u sed m agn etic ballasts.
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Figure 2.A workstation lit with the low-LPD/high-DLQ condition.
Figure 3.Lighting design matrix
Increasing DLQ DLQ 1 DLQ 2 DLQ 3 • • • • • • • • • LPD 1 Increasing LPD LPD 2 LPD3
Gen erally sp eakin g, p erform an ce of com -p u ter-based tasks w as better w h en th e ligh tin g system in corp orated p arabolic lou -vers th an w h en p rism atic len ses w ere u sed . In ad d ition , w h en p articip an ts w ere asked to com p are th eir p erform an ce to th at u n d er th e con d ition s th ey w ere u sed to, th ose u n d er p arabolic-lou vered system s rep orted th at th eir p erson al p rod u ctivity in creased by 8% , w h ereas th ose w orkin g u n d er p ris-m atic-len sed systeris-m s rep orted th at th eir p rod u ctivity w as abou t th e sam e as u su al.
Ligh tin g system s th at in corp orated a com bin ation of task an d am bien t illu m in a-tion w ere given h igh er satisfaca-tion an d ligh tin g qu ality ratin gs th an oth er system s. Becau se th e task/ am bien t com bin ation is frequ en tly ch osen as a strategy to ach ieve en ergy savin gs in ad d ition to th ose
ach ieved by lam p an d ballast ch an ges, th is is good n ew s. Wh en carefu lly d esign ed , en ergy-efficien t ligh tin g can be of h igh qu ality, too.
Re se a rc h a nd Light ing Re c om m e nda t ions
Existin g con sen su sbased ligh tin g recom -m en d ation s receive e-m p irical su p p ort fro-m th is exp erim en t. Th e ligh tin g system s th at w e u se tod ay for com p u ter offices d o h elp p eop le to d o com p u ter-based w ork. Research like th is gives m ore p ow er to th e recom m en d ation s. Alth ou gh th e beh av-iou ral effects rep orted h ere are m od erate, th ey cover im p ortan t beh aviou rs for office
w orkers an d th eir em p loyers. Salaries an d ben efits are on th e ord er of 10 tim es greater th an bu ild in g costs, so th e sm all costs for ligh tin g im p rovem en ts are easily ou tw eigh ed by th e im p rovem en ts in p erform an ce an d satisfaction cau sed by better ligh tin g.
Sum m a ry
A ligh tin g qu ality research p roject con d u cted at IRC d em on strated th at good -qu ality ligh tin g — ligh tin g th at red u ces glare an d u ses electron ic ballasts — is a sm art in vest-m en t becau se it saves en ergy an d con tribu tes to better task p erform an ce an d greater satisfaction .
Re fe re nc e s
1. Am erican Society of Heatin g, Refrigeratin g an d Air-Con d ition in g En gin eers/ Illu m in atin g En gin eerin g Society of North Am erica. (1989). En ergy efficien t d esign of n ew bu ild in gs excep t n ew low -rise resid en tial bu ild in gs, ASHRAE/ IES Stan d ard 90.1. Atlan ta: Am erican Society of Heatin g,
Refrigeratin g an d Air-Con d ition in g En gin eers.
2. Illu m in atin g En gin eerin g Society of North Am erica (IESNA). (1993).
Am erican n ation al stan d ard p ractice for office ligh tin g (ANSI/ IESNA RP-1 1993). New York: IESNA.
3. Rea, M. S. (Ed .). (1993). Ligh tin g h an d book: Referen ce an d ap p lication (8th ed ). New York: Illu m in atin g En gin eerin g Society of North Am erica.
Dr. J.A . Ve itchan d Dr. G.R. Ne w sha m are research officers in th e In d oor En viron m en t Program at th e N ation al Research Cou n cil’s In stitu te for Research in Con stru ction .
For m ore in form ation , con su lt: In tern et: http://irc.nrc-cnrc.gc.ca/ light/lq_project/lqp.html
Figure 4.Examples of the effects of ballast type and luminaire
0 20 40 60 80 100 Glare rating Parabolic louver Prismatic lens Luminaire 2000 1800 1600 1400 1200 1000 Characters typed Electronic Magnetic Ballast Type
“Construction Te chnology Up d a te s” is a se rie s of te chnica l a rticle s conta ining p ra ctica l inform a tion d istille d from re ce nt construction re se a rch.
For more information, contact Institute for Research in Construction, National Research Council of Canada, Ottaw a K1A 0R6
Telephone: (613) 993-2607; Facsimile: (613) 952-7673; Internet: http://irc.nrc-cnrc.gc.ca
© 1997
Nation al Research Cou n cil of Can ad a Decem ber 1997
ISSN 1206-1220
