Light and circadian effects

Janos Schanda1

and

Agnes N. Vidovszky2

1 University of Pannonia

2 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

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Reference

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.