Light and circadian effects
Janos Schanda1 and
Agnes N. Vidovszky2
1 University of Pannonia2 Technical University of Budapest
Overview Introduction The intrinsically photosensitive
Retinal Ganglion Cells (ipRGC) and their effect
Melatonin supression and possible side effects
Lighting and the circadian effect Conclusions and summary
Circadian rhythm - chronobiology
Neuroanatomy of light
From: Brainard GC, Glickman G (2003) The biological potency of light in humans:
significance to health and behaviour. CIE 152:2003. pp. I-22 – I-33.
Chronobiology effects
Influencing the circadian rhythm Jet-lag Shift-work Sleeping disorder
Seasonal affected disorder (SAD)
Early findings 1000 lx 20-30 min exposure:
Decreases melatonin secretion Increases cortisol secretion Increases pulse rate Increases body temperature Decreases pupil diameter Increases alertness Has an effect to decrease SAD syndrome
Action spectrum of melatonin suppression
Some retinal ganglion cells contain melatonin, with a short wavelength visible light absorption spectrum
their excitation influences melatonin secreation into the blood.
Possible regeneration mechanism and spectral sensitivity still not cleard
Alternative circadian action spectrum
Rea-Fiuerio-Bierman-Bullough: Circadian light, J. Circ.Rhythms 8 2010.
Simultaneous broad-band stimulation and pre-stimulation have different effects, still not cleared completly
Early suggestions, 1
Light source with 17.000 K correlated colour temperature
Early suggestions, 2
Change the illumination and CCT during the day in work-places to keep alertness
Negaive effects: possible cancer risk
Possible influence, night time,
outdoor
Rea-Smith-Bierman-Figueiro: The potential of outdoor lighting for stimulating the human circadian systemASSIST 2010
Effect of circ.stimulating radiation on humans of different age
Piazena-Kockott-Uebelhack. Lux Europa 2005.
Questions Should the
intensity evenness correlated colour temperature (CCT)
of artificial light be made variable, so that it looks more similar to daylight?
Has it negative effects if tiredness is suppressed by changing the spectrum of white light?
What is the preferred LED spectrum
Harmonic relationship between CCT and
illuminance
http://www.lamptech.co.uk/Images/Illustrations/FL%20Kruithof%20Diagram.jpg
LEDs used in the present investigation
Calculations, starting assumptions
We tried to keep the CCT of the LEDs near to 2860 K
Intention: use in interior spaces, thus Ra>50 required
To requirements For morning scenes: big C/F ratio For evening relaxation (permit
melatonin secretion) small C/F ratio
19 real LED spectra have been used
2860 K correlated colour temperature was set to optimize the spectra for C/F , using the circadian action spectrum defined by Gall
Computation Determine LED
chromaticity using CIE colour Matching Functions (CMF)
Determine RGB-LED combination spectrum with Excel Solver routine; minimize chromaticity difference
( ), ( ), ( )x y z
0.00.51.01.52.02.53.03.54.04.55.0
350 400 450 500 550 600 650 700 750wavelength, nm
rel.
sp. d
istr.
test_sourceReference
Results: change of Ra Keeping the blue LED spectrum
constant, peak wavelengths of the red and green LEDs for equal TCC, change of Ra.
Circadian effectiveness depends on blue LED spectrum: C/F of LED
combinations For all Red
and Green LEDs the curves are the same
Peak wavelength of Blue LED influences C/F
Conclusions 1 RGB-LEDs using a 470 nm blue LED can
have circadian effectiveness similar to incandescent light
By decreasing the wavelength of the blue LED, the melatonin suppression effectiveness decreases, and the colour rendering decreases too
By increasing the wavelength of the blue LED, the melatonin suppression effectiveness increases, but the colour rendering decreases
Conclusions 2 470 nm blue, 556 nm green and 622 nm
red LED combination provides better evening light than incandescent lamp
490 nm blue, 556 nm green and 622 nm red LED combination provides better morning light than incandescent lamp, but Ra decreases to the minimum permited value
Follow up investigations will be conducted with 4 or 5 LED combinations to increase Ra
Non-additivity has to be studied
Conclusions 3 One can influence the circadian
effect even at low correlated colour temperatures, it is not necessary to use light of extremely high colour temperature
Before trying to influence the circadian rhythm with lighting the possible consequences, mainly cancer risk, has to investigated.
Use light carefully Amber LED light of 10 lx can enable
seeing at night in the bathroom without influencing the circadian rhythm
Figueiro LD+A 2005
Final suggestion The large
screen high brightness modern TV can have an influence on the circadian rhythm: do not use it in your bedroom
Thanks for your kind attention!
This publication has been supported by the TÁMOP-4.2.2/B-10/1-2010-0025 project.
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