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ePaper created 2016-03-29, 15:23:51 | version 1.38.0
feature wellbeing | 29 cosmetic dentistry 1 2016 alsobetween420nmand491nm).Thesecellsproject the synchronisation event to the central biological clock,theyalsoplayapartinthepupilreflexandthey may also contribute to the visual sensation. They are spread all over the retina, but are more numerous in its lower part. They are called the circadian sensor or blue-sky sensor for their high sensitivity to blue and spatial distributionontheretina.Thelatestresearch5 shows thatthesynchronisationsignalisalsoassistedbythe cones, and the exposition time also plays an import- ant part. The effects of two narrowband lights with wavelengthsof460nmand555nmwerecompared: theirinitialeffectonmelatonindecreasewasalmost the same, however, in the case of the green light, the effect ceased after about 90 minutes, while the blue light effect persisted. C1 () hence shows the long-termsensitivitywhiletheC2 ()takestheshort- term effects into account. Two effects are observed: melatonin level decrease and phase-shift of the central biological clock. Figueiro and Hubalek described the construction of a circadian dosimeter (Daysimeter, LuxBlick).6,7 It is a small instrument that is worn like spectacles. Two photodiodes are used as sensors, one corrected by a filter to V() and the second to C(). Measured values are stored along with timestamps in intervals of tens of seconds. Analysis of the data can show whether the user gets a sufficient dose of the light affectingthenervoussystemandwhetherornothe/ she is disturbed by light at night. Critical points can be localised in time so a remedy may be suggested. Datafromadditionalsensorslikeanaccelerometeror a thermometer can make interpretation of the light data easier. Decreasing of the melatonin level in the morning and keeping it low during the day is naturally bene- ficial as it starts a number of processes that lead to higher alertness, activity and concentration. Light sources of higher chromatic temperature can pro- vide spectrum rich in the circadian-efficient band. According to the Kruithoff curve, we can expect the users to require higher levels of light in their place of work, which can be also aided by local luminaries. Higher illuminance and higher chromatic tempera- ture can have tangible economic outputs in the workplace thanks to a better quality of workman- ship8 , lowering stress4 , better use of work time or lowering sick leave. Melatonin is a hormone of sleep andregenerationoftheorganisms.Itscavengesfree radicalsandkillscancercellsinthebody.Soitismost beneficial to let it do its job undisturbed during the night. The means for lowering disturbing night light include a more sophisticated design of street lamps, curtains, window blinds, shutters or red night light. White LEDs are mostly blue LEDs with a phosphor that converts part of the blue light into wideband yellow, which then mixes with blue, making white. This introduces a risk of disturbing the darkness at night by LED streetlights. Blue light gets far more scattered in the atmosphere than the longer wave- lengths, so disturbing scattered light should also be considered.AccordingtotheInternationalDark-Sky Association (IDA), LEDs with a low chromatic tem- perature (2,600 K) are suitable for street lighting.9 However, even in this case, the portion of circadian- efficientlightisthreetofourtimeshigherthaninthe more commonly used high-pressure sodium lamps (see Table 1, page 30). Calculation and measurement Circadian values were introduced in parallel with photometric values by Gall and Lapuente.10 Function V() is replaced with C() and index c is used with the values. In this way, we can consider ‘circadian illuminance’ for example. Circadian illuminance can be measured with a luxmeter corrected to circadian efficiency C(). For coarse relative measurements, a Lee 120 gel filter can be used. Another option is calculation from the spectrum or establishing a factor for converting ‘photopic lumens’ to ‘circadian lumens’foragivenlightsource.Afactorofcircadian efficiency acv (Zircadianer Wirkungsfaktor in Ger- man) is introduced.10 This is calculated for light of relative spectral distribution of power according to Equation 1. acv is a factor for converting photometric values into circadian values for a given light source. It can be used to compare different lights or light sources from the perspective of their effect on our nervous system. The shape of the curve C() and the area under it are not exactly known yet. This is why another factor can be introduced to allow a comparison of the results calculated with the presently known shape of C(), and those based on an updated C() in future. The factor can be defined in different ways, for example the equality of areas under C() and under V() or by the equality of luminous and circadian flux for CIE A incandescent bulb model.10 The option proposed here for discussion is Circadian Activation Index Ac (CAI). Its value is acv{X(λ)} = Km X(λ)C(λ)dλ 380 780 ∫ Km X(λ)V(λ)dλ 380 780 ∫ Ac{X(λ)} =100 XD65 (λ)V(λ)dλ 380 780 ∫ XD65 (λ)C(λ)dλ 380 780 ∫ acv{X(λ)} ≈ 106,25acv{X(λ)} dentistry 12016