J. therm. Biol. Vol. 21, No. 516, pp. 339-343, 1996 Coavrinht ch 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306-4565/96 $15.00 + 0.00 SO306-4!565(%)00019-8 --r,-”
Pergamon PII:
-
EFFECTS OF DIFFERENT LIGHT INTENSITIES DURING THE FORENOON ON THE AFTERNOON THERMAL SENSATION IN MILD COLD YUMIKO TERAMOTO,’ HIROMI TOKURA,‘* KAORI OHKURA,’ YASUE OHMASA,’ SATSUKI SUH0,2 RYO INOSHIRI* and MASAAKI MASUDA* ‘Department of Environmental Health, Nara Women’s University, Nara 630, Japan and *Sharp Energy Conversion Laboratory, Corporate R & D Group, Sharp Corporation, Nara 639-21, Japan (Received 1 March 1996; revised 20 April 1996; accepted 21 May 1996)
Abstract-l. The study aimed at knowing whether thermal sensation during afternoon cool exposure could be influenced by bright light (4000 lx) or dim light (200 lx) in the forenoon. 2. The subjects felt cooler after exposure to dim light than to bright light. 3. Melatonin in the urine was significantly higher in bright light than in dim light at l&30 h and at noon. Copyright 0 1996 Elsevier Science Ltd. Key Word Index: Thermal sensation; bright light; dim light; melatonin
MATERIALS AND METHODS
INI-RODUCIION Subjecjs
et al. (1994) found that the core temperature was maintained at a lower value throughout the day and night when the subjects spent time under bright light (5000 lx) from 6:00 a.m. to 6:00 p.m. rather than dim light (60 lx) at the same time. Furthermore, Kim and Tokura (1995a) showed that the subjects dressed more quickly and with thicker clothing in the evening under the influence of a fall of ambient temperature from 30 to 15°C when they had spent time under dim light (10 lx) from 10:00 a.m. to 6:00 p.m. rather than under bright light (4000 lx) during this period. These results were discussed in terms of different load errors between actual and set-point core temperatures in the bright and dim light conditions. This interpretation suggests that thermal sensation would be different after exposure to bright and dim light even when tested under the identical ambient temperatures, because the set-point of the core temperature might vary by changed rates of melatonin (Cagnacci et al., 1992). The present experiment has been designed to test this prediction by assessing the effects of two different light intensities on thermal sensation during an ambient temperature fall from 31 to 18°C.
Tokura
Ten healthy female subjects participated in the study. They were informed about the purpose of the study and the experimental procedure. Average anthropometric data for the subjects were as follows; age (years): 20.10 f 1.37 (mean &- SD); body height (cm): 160.80 + 2.82; body mass (kg): 51.20 + 2.89; body surface area (m’): 1.48 f 0.04. Body surface area (BSA) was calculated by the following equation (Fujimoto et al., 1968); BSA = WW x Ho.&’x 8.883 x lo-‘, where: BSA, body surface area (m*); W, body mass (kg); H, height (cm). The experiments were conducted at identical phases of the menstrual cycle in each subject to avoid any effects of this on core temperature. Clothing was standardized as half sleeves and half long pants in 100% cotton between the two experiments. Procedure
should be addressed. Tel.: 81/742/20/3469. Fax: 81/742/20/3499.
*To whom corresepondence
The experimental procedure is shown in Fig. 1. The subjects entered the artificial climatic chamber by 9:00 h which was illuminated (200 lx) by fluorescent lamps in the ceiling and with a globe temperature of 28°C and a relative humidity of 50%. The subjects were exposed for 3 h (9:00 to noon) to bright or dim light (4000 lx or 200 lx, respectively at eye level) using fluorescent lamps. A special piece of equipment
339
340
Yumiko Teramoto et al. 31 38 I
5O‘%RH
’
Tlmc of day (hour) t 9
II 10:30
12
0
0
II I I I1 I I I I 1 I 13 13:30 14:30 1530 16:30 17:30 18:30
Light Intensit)
Thermal Sensation Urine Collection
0
Fig. 1. Experimental schedule
(76 cm high, 130 cm long, 20 cm wide) consisting of eight fluorescent lamps (40 W each) was used to provide bright light. In order to avoid the effects of radiant heat from this light source, a transparent acrylic board was set up in front of the light source. During the dim light condition, the light source was turned on but covered by thick black paper, and hence the effects of radiant heat from the light source were removed. During the light exposure, the subjects were required to remain awake and allowed to read a book; they were instructed to look at the fluorescent lamps for at least 1 min every 10 min. The subjects had lunch (350 kcal) at noon and then sat quietly until the end of the experiment under 200 lx provided by the ceiling fluorescent lamps. The room temperature (T,) was maintained at 28°C from 9:00 h to 13:00 h, increased from 28 to 31°C over the courses of 5 min at 13:00 h, and maintained at 31°C from 13:05 h to 14:30 h. Then it was decreased gradually by 1°C every 20 min until the subjects could tolerate it no longer due to the cold-induced discomfort. Air movement was kept constant at 0.2 m/s. Each subject participated in the experiment twice, separated by several days: once with bright light exposure, and once with dim light exposure. The order of the light exposure was random. Measurements
Thermal sensation (Table 1) was assessed on a 13-point scale every 20 min from 1430 h to the end of the experiment. To determine the possible involvement of melatonin in the determination of thermal sensation via changes of set-point of core temperature, urine was collected at lo:30 h, 12:00 h and 13:30 h, and was stored immediately in a freezer. The urine samples for melatonin analysis were analysed at a local hospital. Melatonin was extracted
from the urine samples by diethyl ether. The supematant was evaporated, dissolved in buffer solution, and then analyzed by RIA (Arendt et al., 1984). Sensitivity of the analysis was 2.5 pg/ml. Data analysis
The values obtained were compared by medians, analysis of variance procedure with repeated measures (ANOVA), Speannan Rank Order Correlation and paired t-test. ** and * represent statistically significant differences at the 1% and 5% level, respectively.
RESULTS
Figure 2 shows an individual comparison of thermal sensation between bright and dim light conditions when T. was decreased by 1°C every 20 min from 31°C until the subjects found the cold intolerable. Although there were little differences in
Table 1. Assessment scale for thermal sensation Thermal sensation +6 +5 +4 +3 +2 +1 0 -1 -2 -3 -4 -5 -6
Very hot Hot Slightly hot Very warm Warm Slightly warm Neutral Slightly cool Cool Very cool Slightly cold Cold Very cold
341
Afternoon thermal sensation in mild cold
0 BRIGHT 6 4 2 ()
00.
DIM
6 4
z 0 -2 -4
-2 -4 -6
-6 18 20
6 4
22
24
26
28
30
18 20
22
24
26
28
30
18
22
24
26
28
30
22
24
26
28
30
s2
lii~.I_.r.::_::-:“:
c
18
.-0 %__
20
22
24
26
28
30 6 4 2
s3
18 20
AZ
I-
??
22
24
6 s4 4 2 0 “.“’ -2 -4 -6 i 18
20
6 4
SS
26
28
S8
18
30
20
20
00 0 . 0 . 0 .
..
* . *00.. ?? .*.:a* . 22
08 24
26
28
30
18
20
22
24
26
28
30
18 20
22
24
26 28
30
6 4 2 0
-2 18
-4 -6 20
22
24
Ta(
26
28
30
"C)
-WC)
Fig. 2. An individual comparison of thermal sensation between bright and dim light conditions when T. was decreased by 1°C every 20 mm from 31°C until the subjects could no longer tolerate the sensation of coldness. The open circles present the data from the bright light condition, and the closed circles, the dim light condition.
S-5, S-9, S-10 between the bright and dim light S-l, S-2, S-3, S-6, S7 and S-8 felt cooler
conditions,
in the dim than
the bright
light condition
in the
thermal sensation range from - 6 to 0, even under identical T.. S-4 also felt cooler in the dim than the bright light conditions at T. from 31 to 245°C. Figure 3 compares medians of thermal sensation in the 10 subjects between the bright and dim light conditions. Data between the T. range from 31 to 25S”C have been used because all ten subjects tolerated this range. As clearly seen in the figure, the
subjects felt significantly cooler in the dim than in the bright light conditions in the T. range from 27°C to 255°C (P c 0.05 or less). The slopes of regression lines between T. and thermal sensation in the Tarange from 29 to 25°C (when the thermal sensation was at or on the cold side of ‘neutral’) are individually compared between the two light conditions in Table 2. They were significantly steeper in the dim light (P < 0.05), suggesting that the subjects felt cooler or colder in the dim light condition for an identical fall in T. over this range.
OWI
f68’0
L6Z'I LZS'O PZE'I
8Z6'0 ZE6'0
10'0>d
E6S'81=d
‘1
e
HO’1
fP6’0
69Z’I
fP6’0
ZZO'I IZ9'0 LIO'I IWO S19'0 VIZ.1 LLS'I 861'1 8ZO'I L96'0
f08'0 Z88'0
E18'0 99S'I 189'1 516‘0 L66'1 686'0
SP6'0 8L6'0 fP6.0
906'0 6L6'0
f88’0
‘1
'36'0 LS6'0 i796.0 ZS6'0
If60 016'0
fP6’0
@!I m!a
:v VAONV
ue!paul 01s 6s 8s LS 9s ss PS ES zs
IS
e 19%!1w&w
a%ue~ *J aq u! uoyesuas Ieuuq
3&Z
01 62 WOJJ
pue “J uaa~laq sauy
uo!ssaJftaJ30 sadojs 'i: aIqe1
ayl Bupnp Jam01 r(pu~~3@!s aureaaq amlaladtual iuads pey Layi uayh 3,1c urog 8~ 30 lle3 uoowai3e aJo :sllnsaJ asayl pauuyuo3 (~~661) emyoL pue IEnpeJB e 30 aauanyu! ayl Japun la1003 Lpua~3@!s uua .aJnsodxa Jal3e slnoy IelaAas lnq 6Ia~a!pauuu~ iIa3 wa[qns aqi leyi %upuy 8uysaraiu! isow aqi ln%o IOU pip aJnltzJadrua1 alo3 30 suoynpaJ Jo3 aIq!suodsaJ aJe su~syeywu leo!8olo!dqd 1s~~ asayL .(x1 09) v@g yp uaql JayieJ auryiep iuommma ayl %uunp (XI 000s) @!I iq%uq Japun paceId uaaq paq warqns uaym iq$u pue Lep aqi inoy%o.up Jarno Lpulz~yu8!s awwaq a.weJadural aJo 30 larval aqi iEyi punoj (9661) ‘IV ta amy ~aJniaJadwai aJo @!I ‘JJ!PPue lq+q u! I” 90X1 T P9’8Z Pue Iu’ 86’9 ayj u! saysA lufod-ias pua lewt! uaamiaq JoJJa pleo~ TVV6Z ‘Y OWI le Put? fIur L6’EI 7 8Z’9E pue e 30 sulIai u! sSu!puy asaql passnwp sJoylnt! asayL I” 96’S T 90’SE “4 0O:ZI la :P' L8’OZT ZL’9P pue ‘(xl 0009)~811 @!Jq ql!~ p=duJo:, (XI 01) it@!1 I’JJ E8’91 T EE’6t ‘Y 0E:Ol W fsuo!l!puo:,lq%!l OMl ayi uaawaq awnIon auyn aqi uy sacwaJag!p iue3yu8!s uup 01 pasodxa uaaq @no!aald pvy Laql uaqm 3,Sl ou aJaM aJaq& ‘q OO:Zl pua g 0~:01 ie suoypuo~ Jo “J le %u!ylop Jayyi ql!~ LITD!nb a.xou.IpassaJp 1qQ urrp U! my1 1g%pq U! JaqFiy r(pmy!us!s SBM wa!qns ‘(eS661) eJnyoL pue tug 01 %ufpJo33v u!uoialatu hreu!Jn 30 iunou.uz aqL .suoypuo3 lq%g pue iq%pq uaawaq wa[qns 01 aqi u! u!uoielaw ueaui 30 uosuvduro:, e smoys p aJn%!d .ylw
(x1 cm)
ueq1 i(x1 OOO‘P)@!I mu9 Igun y 00:6 uroq
w!p
lq%!l w!p u! uoou
hr?X!ln
'(01= 4
'(01= u) SO'0> de ‘VAONV dq paz@ua aJaM elea xo!l!puo3 @iy uup :saIsJp pas013 xo!upuo3 II@3 Iq%pq:SaI~J!~UadO'3~S'SZOl 1~UIOJ3'~30 SaSUlTJaql U!ql!Msuop!puo3 1qS!I uup pue l@Jq UaaMlaq sl3a[qns ua) aql u! uoysuas [sulraq$Jo sua!paurJo uospeduro3 V ‘f ‘S!d
SO'0 > d* ‘Isa)-1 paryd B 1(qpazlpzuu aJaM elea ‘uoypuoc~ lqS!IUt!p:SJXq JO102qJE!
