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Artificial Light and Health - A Plea forthe Incandescent Lamp

Alexander Wunsch

Summary

Artificial light brings a large number of benefits tomodern civilization, but there are some aspectswhich indicate that it is necessary to be carefulwith the selection of light sources. Energyefficiency plays the main role in recentdiscussions, but are the light sources with thehighest performance also the most healthy

ones? Mercury-based fluorescent light sources,including so called "energy saving bulbs" as wellas white LEDs with high colour temperature holda great potential to interact with the humanendocrine and circadian system, which can bedetrimental for health under long term conditions.Since the complex light reactions in humans arenow better understood, it is possible to select thespectral composition and electromagneticproperties of an artificial light source in order toavoid detrimental side effects and to achieve amaximum of positive effects on human health.

Introduction

Since the very beginning of life on earth, sunlightaccompanied all biological processes andevolutions. Therefore, from the biological andalso medical viewpoint, sunlight is the archetypeof natural and healthy light. Life on earth is highlyadapted to the spectral properties of sunlight. Forhumans there is another lightsource given bynature, which is the fire our predecessors andancestors had in use since about 1,5 millionyears as a source of light and warmth. Sunlightand fire have an important common ground -both spectra are located on the Planck curve or

black body curve. From the physiological point ofview one can say that a radiation sourcebehaves naturally, as long as the given spectrumfollows the Planck curve. Using this definition, alllight sources that we had in use until 1906, theyear the mercury discharging lamp had beeninvented, were natural: chips of pinewood,blubber-oil lamps, candles, kerosene lamps,gaslight and even the incandescent and halogenlamps. The Planck curve enables us to predictthe spectral distribution of a light source, as longas we know the temperature: All these classicalartificial light sources show a very low content ofultraviolet radiation between 0 % (candle 1800 K)

and 0,4 % (halogen lamp, 3200 K) compared tosunlight (> 11%, 5700K).

Tab. 1: Therapeutic ranges in sunlight spectrum

Light and Hormones

The sun spectrum can be split into three parts:UV, VIS and IR. The visible part is obvious, theother two parts are invisible - and this is theproblem, nature had to solve: making theinvisible parts detectable before they can unfoldtheir destructive potential in the body rsp. on theskin. Hereby the IR part can be detected

immediately by thermal receptors in the skin. Thephotochemical reactions induced by the UV arewell known and examined, while the human bodyhas no specific receptors for this kind ofradiation. UV effects show a typical delay ofseveral hours after exposure, which takes themout of reach of behavioural adaption. When youstart to feel sunburn, it is too late for prevention,the reaction cascade is already running. Thesymptoms of the UV overdose are swelling andleakage of the dermal capillaries, inflammation,pain, destruction of dermal tissue, DNA andhormones. In case of severe sunburn up to 60%

of the blood can be shifted into the skin, leadingto a life-threatening circulatory shock state. Inorder to counteract those destructive effects, thesystem somehow has to foresee what couldhappen. Therefore it was practical that thesunlight spectrum follows the Planck curve:within this given framework the human systemcould develop a specific sensory system which isbased on the factum that high content of UVradiation in nature is always linked to an evenhigher content of blue. The novel receptorsystem discovered by Brainard, Thapan andothers is an extrapolative UV detection systembased upon the reception of blue light in the

ganglion cell layer of the retina. Some of theseganglion cells contain a pigment called

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melanopsin, which is receptible for blue rays, theabsorption spectrum peaks around 460 nm. If the

human retina detects bright light with a highcontent of blue, a cascade of endocrine reactionsis triggered: Activation of the hypothalamus andthe pituitary gland inducing a systemic stressreaction in the sympathetic part of the vegetativesystem and a suppression of theparasympathetic part including the activity of thepineal gland. In terms of physiology the two lightfactors, brightness and bluishness, induce ahormonal stress reaction capable ofcounteracting most of the destructive effects ofthe UV radiation.

Unnatural Light Sources

All light sources which do not follow the Planckcurve in their spectral characteristics thereforecan lead to a malfunction in the humanendocrine system, as long as they produce brightlight with a high content of blue rays. Thecorrelated colour temperature (CCT) gives novalid information regarding the content of blue:even warmtone fluorescent lamps with a CCT of2700 K show a unnatural peak in the blue part ofthe spectrum which is able to trigger thehormonal stress reaction. From the viewpoint ofphysiology it is highly recommendable to use

incandescent light sources instead of fluorescentlights in order to avoid unwanted hormonalmaladaption/malfunction.

Tab. 2: Spectral comparison of true colortemperature (tCT) of an incandescent lamp (IL)and correlated color temperature (cCT) ofcompact fluorescent lamp (CFL).

Blue Light and Vision

The human eye has two pathways for theprocessing of light signals. The optical part isresponsible for vision processes while the

energetic pathway controls the endocrinereactions via the retino-hypothalamic tract. For

the purposes of vision it is better if thesurrounding light does not contain high amounts

of blue and violet wavelengths. The higherrefraction for short wavelengths which occurs inoptical media also appears in the eye. Thiscauses a chromatic aberration effect with

Tab. 3: Chromatic aberration dependent fromwavelength.

negative consequences for sharp vision. Thedifferent wavelengths focus on different planes inand around the focus plane of the retina. Due to

photooxidative effects, the blue and violetradiation also promotes chemical reactions in theoptical media of the eye and in the foveacentralis. We find a number of mechanisms inthe eye which provide better vision on one handand less photooxidative stress and damage onthe other, in order to reduce the negative effectsof blue light on vision. First the number of bluereceptors is up to 20 times less compared to thenumber of red cones in the fovea centralis.Secondly there is a concentration of lutein, ayellow pigment which filters out excrecentportions of blue and shows also antioxidativeproperties. The concentration of this protection

substance is reduced in the eyes of elderlypeople. Ophthalmologists have discovered thatthere is some evidence that the age relatedreduction of lutein is functionally compensated bythe increased blur in the lens, which is alsopromoted by blue and ultraviolet light. As aconsequence they replace the lens in cataractsurgery by a colored one, which filters out theblue portions in order to protect the macula fromfurther degeneration. This shows that even thestructures of the eye wear out, depending on ageand the amount and quality of light which has tobe processed during a persons lifetime. The

question is, is it only sunlight which isresponsible for the increasing incidence of age

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related macular degeneration, which is found in30% of the population over 70 years of age in

industrialized nations? These people stay 90% oftheir time inside buildings while under theinfluence of artificial light, which has to be takeninto account as well. We indeed find that there isa large and increasing number of fluorescentlight sources in our environment which producehigh amounts of photooxidative potent light, suchas mercury vapor lamps with high colortemperature, the backlight of TFT computerscreens and TV sets.

Tab. 4: Spectral ranges responsible for retinaldamage and repair correlated with spectralenergy distribution of different lamp types.

The fluorescent lamp spectrum does not containsignificant amounts of long wave radiation suchas deep red or near infrared. A number ofexperiments with wavelength > 650 nm haveshown that they have the potential to repair theoxidative damage caused by blue and violet lighton cellular levels. Again - if we compare thespectral constitution of energy saving lamps andother fluorescent light sources with theincandescent lamp spectrum, the latter showsclear advantages in terms of better vision andretinal protection and repair.

References

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Contact

Alexander WunschBergheimer Strasse 116

69115 HeidelbergGermany

wunschart@mac.com