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Lights Should Support Circadian Rhythms: Evidence-Based Scientific Consensus

Authors:
  • Circadian Light Research Center

Abstract

For over a hundred years, the lighting industry has primarily been driven by illumination aesthetics, energy efficiency and product cost with little consideration of the effects of light on health. The recent widespread replacement of traditional light sources by blue-enriched LED lights has heightened concerns about the disruption of the blue-sensitive human circadian system by these LED lights and their impact on the multiple health disorders linked to circadian disruption. Despite these health concerns, less than 0.5% of the lighting sold today modifies spectral content and intensity between day and night. We report that 248 scientists, with a total of 2,697 peer-reviewed publications on light and circadian clocks since 2008, reached consensus on 24 statements about the impact of light on circadian rhythms and health based on accumulated scientific evidence, including support for the widespread introduction of circadian lighting and warning labels on blue-enriched LED lights indicating that they “maybe harmful if used at night”.
LIGHTS SHOULD SUPPORT CIRCADIAN RHYTHMS: EVIDENCE-BASED SCIENTIFIC CONSENSUS
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(1*&*.1"&&(**E "=79+,
 .*JK,&&("*&"77  ,("
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0M,E*,(,(" ,E*,&&((1
&..(+J%<K"77>.,4&&+
/(NF/H0(&"+!&&F0!HJ<K&+"
(L..&&,**11F(,*H, &&(1, 
* (&,&.  &(, 1+,
&&,*("+.(+&,(1"
1*,&*"&&&&&&
,&1&&*&&J8=K
&7&&((1+ 1",&+("("4&'
F( O(H(*((,"+&*,+4&
(,&&,(&&(3'P,&(J7K. '
(* N4&&"1",N(1,.&&*&(+1,&
;D7
.(*&, & *,&+(JKE*,1,&'(
((,(:&,1&,, &&" ("
1,(%;7 *"+ *&&"*
((&F*!QH,   ,+1,&.'
(,(&,,&&,&&,*&+J%
8K
-1,,*1,&(,(" *&&" 
1,*((*&(&&,*J<K.R77
1S"((,"1".1%,,&,+
&1,'('789+(""&&,**
**J>K
& T,:&1"((,"+((N+1,'(
& &&&&" ,., *1","((
&:,( +&:&&,&1&, 1.
&,"&&.&.,&+"&:(+&&((&&
&1&&,&&,"1&+ &&
METHODS
Survey Popula!on:
&+,1. ?&&@C?(@:777*.&:&
&*,11.*77;*71"=%88,M,,:
,,+ *.*,1+, *.&.1,
 +8%,,( &:1 & &
;D7
*,1.1+8<F8>9H+&:&,&* 
*&*&:&,,"&'(%;F89H+
&*& *,"F89H
-%;**,1(+F A>U(A%<;H*.&
 ?&&@C?(@&77;G7,"*++
*F%%;9H.1$ &=<F;>9H.1,*>F<=9H.
1, &F%;9H.1,S$.V7F%79H.1
 (F7;9H.1+&-*,1&+&+%;*.
.&+"*I* "& A, &F,&,(
, ,1T&, .&H, &F,
&,(  1*&1*&,S &," H
-.7&.* "*+ , &%8&.
*+ , &",1(,*& *++M,&+**
+& .&,&,(&M,
Survey Design
3" .*+(1",+&-".*+&,
&&,, N(&:&,.+.(**AHIW.H
$&H' &%HQ&8H13.**&&
&&&,1,((. +**-: ( 
.*E**&" 1&:&,.+.(*
*AHIW.H("(H(%H(8H("(
De&ni!on of Consensus
;D7%
0((,*+&(& *E&:&M,&(, ,
( +1E*&0**&"&,,.
,++1&1.*&*1(*&*&( :
.1.T,( +*>7>89( L&&*
&,J;=K0(,".**,".1
+1&+ *&*.:&,..+*
F<<>9H,** -*?Q&@?1@.
& 1+&1 ?(@?("(@.& 1+E*
*&" -?IW.@*& .&1+
,+(+&*&:&*&..&".+ 
+1E&,+ &,&&,*&
RESULTS
,.&%,+%7 -1
-:+&, +(,E*,1((,(
"F"(1(&&(H&(1, +&&" 
 (-.(&,1,&&"  *+
F=89H,*(&&" &&,F=;%9H-.
&,&(" (". "(+87
877,E&&& (&&" F>789H *
" ,&*F>%>9H- T"F8=9H+*&
.?(&@.?.1@&(" ("&
*(1,&.&,
;D78
CONSENSUS STATEMENTS 9
!1,&&"  *+ (( =8
,*(&&" &&, =;%
!(,"E*,"(&&& (
&&"  =8
!(,"E*,"(&&*( ;<%
Increasing indoor light intensity during day!mea:
X&&&& (&&"  >78
X& *" ,&* >%<
Increasing indoor light intensity at nightb:
X&,*+&&"  =7<
X&,**+&, *,& =%<
Repe!!ve and prolonged exposure to light at night bright enough to cause circadian
disrup!on:
X&+1&&.  <><
X&+1"1 >%>
X&+* ;>%
Human Sensi!vity to Blue Wavelengths
-"*+*!Q *&&*, 
**E "%;7 1,*+1*&,  =>
- *.(+&& %<7%=8 1,(
"*+*!Q *&&* =>
Blue-enriched (460-495nm) light in the evening (during the three hours before
bed!me)c
X,*&,* 1,*( " >7
X*"&&"  1,*( 
" >88
X,*&&"  1,*( " >7
Exposure to 460-495nm blue light at night:
X,** *,& =7<
X,*&&"  ;%;
PRACTICAL APPLICATIONS
'(,(F,(,1+1 H,5
1,&*&&"*1 ;8
-+&&,*,(,1+1 &1,&
1"H (((.& "& * 1"*+ ,
.H,&(1,&+(( "
M,+, >7
EXPERT OPINION
-1,&+((" ,&  * (
&&,& && *,F-H+(
,& ;<>
0&(("4&&"+(11,+&+
&,(&&,*, =
'(.(%<7%=8 1,&,&".(1? "1 >=
;D7<
 +,+,(@
-.,4&&,**.*,&+&&
((T,("1,&&"( 
1,&&  ;8=
-(:&,"(+&&((
,1* N.*1,(*N, =7<
, (+ (+87877*,E, & *1*(E*,
"
1, (+ (+87877,E, & *1*("
&, (1(,(F77877*,EH:*1
-1A .&&,.&
-&+&,  *&+&&((-.(
&,&(("(&,*+&&" 
F=7<9H&,**+&, *,&F=%<9H-.
&,**(E*,((1(,(&,&&
,*&+1&&. F<><9H1"1F>%>9H*
F;>%9H- T"+*(.(,**F?(&@
?.1@H**(E*,((.1(,(
&,&&,*&&&,F<7>9H*F<7;9H1,
&.&,
-+&,  *&+1,.(.
, , &&" -.(&,?"*+
*!Q *&&*, **E "%;7 1,*+
1*&, @F=>9H? *.(+&& %<7%=8
 1,("*+*!Q *&&*@F=>9H
;D7>
-.&,?1,&F%<7%=8 H((F,(,
1+1 H,*&,* F>79H*"&&"  F>889H
,*&&"  F>79H1,*( "-.
(&,E*,%<7%=8 1,((,** *,&
F=7<9H,*&&" @F;%=9H
-+,+&, *&&**&+&&&&
((-.&,?(,(F,(,1+1 H
,51,&*&&"*1@F;89H?+&&
,*,(,1+1 &1,&1"H (((
.& "& * 1"*+ ,.H,&(1,&+
(( "M,+,@F>79H
-*&*.E**1, *&+&&&&+
( * +((-.&,?1,&+((
" ,&  * (&&,& &&
 *,F-H+(,&@F;<>9H?&(("4&&"+(
11,+&+&,(&&,*,F=9H
, N(E**.&,?.,4&&,**
.*,&+&&((T,("1,&&"
( 1,&& F;8=9H?'(.(%<7
%=8 1,&,&".(1? "1 +,+,(@F>=9H-"
&&,?(:&,"(+&&
((,1* N.*1,(*N,@F=7<9H
;D7;
NO CONSENSUS %
;D7=
Increasing indoor light intensity during day!med
X&&*( 8==
Repe!!ve and prolonged exposure to light at night bright enough to cause circadian
disrup!on:
X&+*&&  %%
&+&&, <7>
X&+* <7;
Increasing the 460-495nm blue content of indoor light during day!mee
X&&&&  <<
X&&*( %>
Repe!!ve and prolonged exposure to 460-495nm blue-enriched light during nocturnal
hoursf
X&+1&&.  %>8
X&+*&&  =
X&,& " *(,&& 87<
X&+&&, %=
X&+* %8;
X&+* <8%
PRACTICAL APPLICATIONS
'(,,((L,51,&*&&"
*1 8%=
)(1(1,&(,((L "&1,
+&,(&&,*, 8<%
'((.(1,&,("  1,&,(
((*&+.%S>.*& 87;
, (+ (+87877*,E, & *1*(E*,"
, 0("+77*,E .,.., & *1*("
+, 0((+77877*,EM,*+  .
-1A .&&,F,**1".+*H.&
;D7 7
-1 +.&.F<<<9H&,.& *
1.*+M,&+.,1(,**.&.*"
, &*.", &..
(( 1..,1(,*.(:&6&1(+,,
+"+,++" -+ +.A
0&(("(&,**+&, 
*,&
E*,%<7%=8 1,((,** *,&
-(:&,"(U+&&((,
1* N.*1,(*N,
(&,&, , &F1,&&,
1,1(,*H
/ A
!**(E*,((1(,(&,&&,*
&+&&,, &,1(,*
1(" ,**F&&,&, &
,1(,*H
0)0/$
 (%;&*&*. ,**.*,1&&&(:
 . ( &,  ?        
   
@-&&,.,**1"&,
;D7
*&:&   1,  ,*6& && "    +*&"
1,&((&+M,(,("-&:&E*
( ?    !"#       $
@
,&'(( &(( 1&,"&*77
77, * .5(" 4&((& *8, S.5+&&87<7
, S.5+ P,&( J<K - 1,(   ((,( (, 
FQ$H&".&(N1"7%$1N+"&.#*&
0 , ,T$ ,JK,&'(.+ 
9 7(;79 71"( *&
," 1  &N  *&  +  (( . '  & ("
(+,* 1"(,"1&&(P,&((J7
K
/  + ,1&&&, ,,&,+1,&
'( "1N,, -&&&&(, (+
*"(&*&.molecular & :1"7>$1N"("
&.#6"&!1&Y,(J7K,M,"1,
(JK-1&, *&&"*((&F*!QH
&&&& (&"&*"Z%;7 1,
(JK  ,+1,&.'(,(&,,&&,
&&,*&+J8KE*,&&((
1&.1"1&&,&&&&,(1
*&&,*&:&*+/0(&"+!&&
;D7
F0!HFK &&&J;K$0$-E&("( J=K 
E*,((,4&(,("&+1&&

,&,,"1&,((,"1".,&
&&((& (&&,4&" , &
1& &*&"."".: *+((
,"*& (".-+*+1.
&,&1& ,"+&&&:-**,.
*&*,,".&&.*,1+, *
.&:,1&. ?&&@C?(@&77;FL
:*+/0!&&(&:(J<KH+. ..1+"
 -.*&+**&*1"&.
&.&( *"  .,+..
&*(,. *,1&..,4&"
+ .((,(.&,".&,& "1,*
 *
3,&.&,8  "
+&,"&&3;+  T"F87<G<8%9H+* 
?(&S.1@1,,4&+&+* (
? &@1(&,1..F<<<9H,**&0
(,*+&&(((+,(+& "11.
&? &@..&T,:+ &
;D7
*1&++ ".&,*&:&,&,1
&. ?&&@C?(@&,"E&777S"
&*&((1* +1,*'(+
&,,%;7 1,&'(+" .,(:&"& * (&
("4&&"J<K- 5E&,,((.& :1,
&""(&"&!& +(:&,
 &&((,&%9,&"+,&*
(,( J%8K * +*,&+, &
*J<>K.*&&((+ ?&@? ,@
!3!$
 ,N 33,%&'%%()*&
%+, 1(A)"U=;
 W*$$/5!-$, &"5,"F$HA
,&+(E*, *,-./77U
11A8
 -3'W[$!#&6&+&,*/,0,*,
7<U78AG
% ,&"!-Q[:#&(*01+, 
&1 Q.1"$&,(AM,&+0
,*1"'($(! 0(&-*77=U8: %>G8
8 W 2,-,'(((&.1"1
"**7U
5*ASS& &,*& S*S&&SS77=S*SN&7S<<7;=8\(],H
;D7 %
< ,!,5W'." (1(( (&
.*"&&A1T&(,"^;8777)W1*&**
7U5*ASS... E(S&S77S77<;7=%+,*+
> +W!QY,&(&"+L.*(::((
12 348:7<87<<
; !QQ6&+(O ((A& 
 &&&*&" /,-,*,57U45A%G%<
= )$-E&("( $-&N *(L.
(($-E&("( )* +, &7U
5*ASS*(S*S,S*,1S&&_ S:77%77_87;*+
7 )* +("7787=("( A:+Q
&' *U3,7U5*ASS...(,(S&, S!7--77
77
 +7;W 1"3,& *A1,A*17U
5*ASS(&& SS&S7;SS7%7
 ,*)7;U5*ASS&,*,S+S.S.(1,1,.1,
("(*,&(( 7;,(_
 Q1"$1+1,',N((6,7%U514A8G8
% V1.W((6,7;U553A>%><
8 &Q2+( ((" *&&&
" *+70,77U10: =7
< ' ,*&"1&, &&*,&"
("4&&"'(N7
;D7 8
5*ASS... (N& S((.1(S&S%===%S(( ,
1& ,*1T& (N
> (8&05'9:%;2 2<,2 2=4
5*ASS...1( && S*S(1&&" (( 
; !6'Q 2$,* ( +1,&*
*1&,("A&,(,+10,2 =3)13A7=87=
= Q,Q$,'[Q N#,* A 
&&(\%;+&7U163A7%;%
7 2''',&-3Y,(-&&&&&&,(,A
'+ $1N"("&7>-7;U39A
<G=
  [Q,5,!&*&"*&, .EE*,
*"& &.'(,.*&&->077U35A%78G%8
 #[',&!#,  *+ *(  E "1,(F` E
Z%>= H,**(&+QMSQS((&&*0+>,7U280A
7=;>
 0(&"+!&&?'8&
0')+@',*A;7A+@'77U98A8<><%
% Q'W#0 *&+)*('((3 
!#7U*5*ASS(S77<STT 77<7
8 3(,Q&',-(( * ,+*
*(*.N I ((
 &+&&:/7%U9A8>G8>
;D7 <
< (.30#,(Q,-6&+&"&((&,*
&"*"(&* A*,":B&&67>U41A<G

>  W'T!#3( " &(**&*",&
&&,+, &*A N&,"
05,2 =44A=%7
ACKNOWLEDGMENTS:
!Q,5,+&."+,11#',(
Q+&.(*&(+&,,"
+*+,&,
3,(A3+,(a,,".1*&+& *( 
1.*1"W,0&
,&1,A&&(,"!#
&1,.(&+ "N,"
*L!# ,&*
COMPETING INTERESTS:
[*)=;>%%7$78<878=;%#<=<<=
=7;<8=W!7=;<>77)7;%7<***&-S)7=S7%>;
(W,0&&&&* N*&"((,&&,(
"('&& *+ M,"W,0&0!0$
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Summary. For billion of years, alternating light-dark cycles have influenced all biological functions, and living organisms have developed evolved internal circadian clocks capable of adapting to cyclical 24-h fluctuations in the environment. In the modern era, the advent of electric lights allowed light during night hours, and the introduction of less expensive light-emitting diodes (LED) sources favored a widespread increase of light use in at least 80% of the world. However, exposure to artificial light-at-night (ALAN) is associated with a wide spectrum of health problems. We analyzed recently published available literature, including two systematic reviews and one meta-analysis, to investigate the possible existence of sex-specific differences in the effect of ALAN exposure on mental health disorders, sleep problems, and cardiometabolic disorders. We found twelve studies (n = 160,305, 20.8% females) focusing on mental disorders, ten studies (n = 591,554, 44.4% females) focusing on sleep disorders, and ten studies (n = 588,929, 49.8% females) focusing on cardiometabolic disorders. On the one hand, the majority of studies included a valid percentage of females, but only a few studies performed separate analysis by sex. Thus, although the available evidence seems to confirm some negative effects on biological functions under the control of circadian rhythms, no definite conclusions can be drawn on the existence of possible sex-specific differences. The impact of light pollution on human health remains a fascinating area of research, and furher studies are needed to definitely confirm this relationship, especially studies providing robust evidence of possible sex-specific differences.
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The regular rise and fall of the sun resulted in the development of 24-h rhythms in virtually all organisms. In an evolutionary heartbeat, humans have taken control of their light environment with electric light. Humans are highly sensitive to light, yet most people now use light until bedtime. We evaluated the impact of modern home lighting environments in relation to sleep and individual-level light sensitivity using a new wearable spectrophotometer. We found that nearly half of homes had bright enough light to suppress melatonin by 50%, but with a wide range of individual responses (0–87% suppression for the average home). Greater evening light relative to an individual’s average was associated with increased wakefulness after bedtime. Homes with energy-efficient lights had nearly double the melanopic illuminance of homes with incandescent lighting. These findings demonstrate that home lighting significantly affects sleep and the circadian system, but the impact of lighting for a specific individual in their home is highly unpredictable.
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Electric light has enabled humans to conquer the night, but light exposure at night can disrupt the circadian timing system and is associated with a diverse range of health disorders. To provide adequate lighting for visual tasks without disrupting the human circadian timing system, a precise definition of circadian spectral sensitivity is required. Prior attempts to define the circadian spectral sensitivity curve have used short (≤90-min) monochromatic light exposures in dark-adapted human subjects or in vitro dark-adapted isolated retina or melanopsin. Several lines of evidence suggest that these dark-adapted circadian spectral sensitivity curves, in addition to 430- to 499-nm (blue) wavelength sensitivity, may include transient 400- to 429-nm (violet) and 500- to 560-nm (green) components mediated by cone- and rod-originated extrinsic inputs to intrinsically photosensitive retinal ganglion cells (ipRGCs), which decay over the first 2 h of extended light exposure. To test the hypothesis that the human circadian spectral sensitivity in light-adapted conditions may have a narrower, predominantly blue, sensitivity, we used 12-h continuous exposures of light-adapted healthy human subjects to 6 polychromatic white light-emitting diode (LED) light sources with diverse spectral power distributions at recommended workplace levels of illumination (540 lux) to determine their effect on the area under curve of the overnight (2000–0800 h) salivary melatonin. We derived a narrow steady-state human Circadian Potency spectral sensitivity curve with a peak at 477 nm and a full-width half-maximum of 438 to 493 nm. This light-adapted Circadian Potency spectral sensitivity permits the development of spectrally engineered LED light sources to minimize circadian disruption and address the health risks of light exposure at night in our 24/7 society, by alternating between daytime circadian stimulatory white light spectra and nocturnal circadian protective white light spectra.
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Life on Earth evolved in day-and-night cycles. Plants and animals, including insects such as the fruit fly, have a biological clock that controls their circadian rhythms — as the 2017 winners of the Nobel Prize in Physiology or Medicine showed. Now, humans’ increasing reliance on artificial lighting is changing those rhythms.
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Background The frequency of metabolic and bariatric surgery (MBS) is increasing worldwide, with over 500,000 cases performed every year. Obstructive sleep apnea (OSA) is present in 35%–94% of MBS patients. Nevertheless, consensus regarding the perioperative management of OSA in MBS patients is not established. Objectives To provide consensus based guidelines utilizing current literature and, when in the absence of supporting clinical data, expert opinion by organizing a consensus meeting of experts from relevant specialties. Setting The meeting was held in Amsterdam, the Netherlands. Methods A panel of 15 international experts identified 75 questions covering preoperative screening, treatment, postoperative monitoring, anesthetic care and follow-up. Six researchers reviewed the literature systematically. During this meeting, the “Amsterdam Delphi Method” was utilized including controlled acquisition of feedback, aggregation of responses and iteration. Results Recommendations or statements were provided for 58 questions. In the judgment of the experts, 17 questions provided no additional useful information and it was agreed to exclude them. With the exception of 3 recommendations (64%, 66%, and 66% respectively), consensus (>70%) was reached for 55 statements and recommendations. Several highlights: polysomnography is the gold standard for diagnosing OSA; continuous positive airway pressure is recommended for all patients with moderate and severe OSA; OSA patients should be continuously monitored with pulse oximetry in the early postoperative period; perioperative usage of sedatives and opioids should be minimized. Conclusion This first international expert meeting provided 58 statements and recommendations for a clinical consensus guideline regarding the perioperative management of OSA patients undergoing MBS.
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Disruption of circadian rhythms, provoked by artificial lighting at night, inconsistent sleep-wake schedules, and transmeridian air travel, is increasingly prevalent in modern society. Desynchrony of biological rhythms from environmental light cycles has dramatic consequences for human health. In particular, disrupting homeostatic oscillations in endocrine tissues and the hormones that these tissues regulate can have cascading effects on physiology and behavior. Accumulating evidence suggests that chronic disruption of circadian organization of endocrine function may lead to metabolic, reproductive, sleep, and mood disorders. This review discusses circadian control of endocrine systems and the consequences of distorting rhythmicity of these systems. Expected final online publication date for the Annual Review of Physiology Volume 78 is February 10, 2016. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
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Objectives Falls in care home residents have major health and economic implications. Given the impact of lighting on visual acuity, alertness, and sleep and their potential influence on falls, we aimed to assess the impact of upgraded lighting on the rate of falls in long-term care home residents. Design An observational study of 2 pairs of care homes (4 sites total). One site from each pair was selected for solid-state lighting upgrade, and the other site served as a control. Setting and Participants Two pairs of care homes with 758 residents (126,479 resident-days; mean age (±SD) 81.0 ± 11.7 years; 57% female; 31% with dementia). Methods One “experimental” site from each pair had solid-state lighting installed throughout the facility that changed in intensity and spectrum to increase short-wavelength (blue light) exposure during the day (6 am–6 pm) and decrease it overnight (6 pm–6 am). The control sites retained standard lighting with no change in intensity or spectrum throughout the day. The number of falls aggregated from medical records were assessed over an approximately 24-month interval. The primary comparison between the sites was the rate of falls per 1000 resident-days. Results Before the lighting upgrade, the rate of falls was similar between experimental and control sites (6.94 vs 6.62 falls per 1000 resident-days, respectively; rate ratio [RR] 1.05; 95% CI 0.70–1.58; P = .82). Following the upgrade, falls were reduced by 43% at experimental sites compared with control sites (4.82 vs 8.44 falls per 1000 resident-days, respectively; RR 0.57; 95% CI 0.39–0.84; P = .004). Conclusions and Implications Upgrading ambient lighting to incorporate higher intensity blue-enriched white light during the daytime and lower intensity overnight represents an effective, passive, low-cost, low-burden addition to current preventive strategies to reduce fall risk in long-term care settings.
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We examined whether giving feedback to participants in a Delphi study about the level of agreement across the expert panel had an effect on opinion change between rounds. We also considered the potential influence of participants’ sociodemographic and professional characteristics. Five three-round Delphi studies were conducted independently, in which a total of 628 mental health experts responded to all three rounds. In each study, participants had to decide, based on their experience, whether a series of categories were relevant. The percentage of group agreement (i.e., percentage of participants who considered each category as relevant) in round 2 was shown as feedback in round 3, and responses in rounds 2 and 3 were considered to analyze opinion change. Results showed that when the feedback given in round 3 indicated that ≥75% of experts considered a category to be relevant, there was a further shift in opinion towards the group opinion (i.e., the category then yielded even greater consensus), whereas if the feedback indicated <75% group agreement, individual opinions tended to shift against the group opinion (i.e., consensus over the category decreased). Neither sociodemographic nor professional variables had a significant effect in explaining opinion shift. These results show that in Delphi studies, feedback has an influence on individual responses and the achievement of consensus. https://authors.elsevier.com/a/1cAL2_wSRHf5E
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Patients in intensive care suffer from severe illnesses or injuries and from symptoms related to care and treatments. Environmental factors, such as lighting at night, can disturb patients’ circadian rhythms. The aim was to investigate whether patients displayed circadian rhythms and whether a cycled lighting intervention would impact it. In this pilot study (N = 60), a cycled lighting intervention in a two-bed patient room was conducted. An ordinary hospital room functioned as the control. Patient activity, heart rate, mean arterial pressure and body temperature were recorded. All data were collected during the patients’ final 24 h in the intensive care unit. There was a significant difference between day and night patient activity within but not between conditions. Heart rates differed between day and night significantly for patients in the ordinary room but not in the intervention room or between conditions. Body temperature was lowest at night for all patients with no significant difference between conditions. Patients in both conditions had a natural circadian rhythm; and the cycled lighting intervention showed no significant impact. As the sample size was small, a larger repeated measures study should be conducted to determine if other types of lighting or environmental factors can impact patients’ well-being.
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Background: Disturbed circadian rhythm is a potentially modifiable cause of delirium among patients in intensive-care units (ICUs). Bright-light therapy in the daytime can realign circadian rhythm and reduce the incidence of delirium. We investigated whether a high-intensity dynamic light application (DLA) would reduce ICU-acquired delirium. Methods: This was a randomised, controlled, single-centre trial of medical and surgical patients admitted to the ICU of a teaching hospital in the Netherlands. Patients older than 18 years, expected to stay in the ICU longer than 24 h and who could be assessed for delirium were randomised to DLA or normal lighting (control), according to a computer-generated schedule. The DLA was administered through ceiling-mounted fluorescent tubes that delivered bluish-white light up to 1700 lux between 0900 h and 1600 h, except for 1130-1330 h, when the light was dimmed to 300 lux. The light could only be turned off centrally by investigators. Control light levels were 300 lux and lights could be turned on and off from inside the room. The primary endpoint was the cumulative incidence of ICU-acquired delirium. Analyses were by intention to treat and per protocol. The study was terminated prematurely after an interim analysis for futility. This study is registered with Clinicaltrials.gov, number NCT01274819. Findings: Between July 1, 2011, and Sept 9, 2013, 734 patients were enrolled, 361 in the DLA group and 373 in the control group. Delirium occurred in 137 (38%) of 361 DLA patients and 123 (33%) of 373 control patients (odds ratio 1·24, 95% CI 0·92-1·68, p=0·16). No adverse events were noted in patients or staff. Interpretation: DLA as a single intervention does not reduce the cumulative incidence of delirium. Bright-light therapy should be assessed as part of a multicomponent strategy. Funding: None.