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Opt. Pura Apl. 50 (2) 165-172 (2017) © Sociedad Española de Óptica

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Type:ResearchpaperSection:VisionSciences

Spectralradianceofbluelightfiltersonophthalmiclenses

Radianciaespectraldelentesoftálmicasconfiltrosdeluzazul

CristinaFernández,MarcArgilés,ElisabetPérez-CabréS*,GenísCardona1.SchoolofOpticsandOptometry,UniversitatPolitècnicadeCatalunya,

VionistaVellsolà37,08222Terrassa(Barcelona)(*)E-mail:[email protected] S:SEDOPTICAmember

Received:30/12/2016 Accepted:29/05/2017

DOI:10.7149/OPA.50.2.49072

ABSTRACT:

Asaresultoftherecentimprovementinlight-emittingdiode(LED)technology,thedisplaysofthevastmajorityofelectronicdevicesarenowilluminatedbyLEDs.Thereareseveraladvantagesofthistypeof light source over its predecessors; however, recent research is giving support to the fact thatprolongedexpositiontothewhiteLEDsemissioninthebluespectrummayhaveanegativeimpactonvisualhealth,aswellas,onbiologicalrhythms(circadianrhythms).Asaconsequence,ophthalmiclensmanufacturershaverecentlyintroducedinthemarketinnovativelensesthatincorporatebluelightfilters,especiallydesignedforelectronicdeviceusers.Inthiswork,theperformanceofdifferentbluelight filterspresentoncommerciallyavailableophthalmic lenseswas testedandcompared.LenseswereplacedinfrontofaLED-basedbacklighttablet,inasimilarwayacommonuserwouldbereadinga text on the electronic device. The absorption characteristics of the various samples from fourdifferentophthalmiclensmanufacturersweremeasured.Analysisofthedifferentsamplesfromthesamemanufacturerwasconductedandbluelightfiltersfromdifferentmanufacturerswerecompared.Keywords:Bluelightfilters,ophthalmiclenses,LEDbacklightscreens,electronicdevices,circadian

rhythm

RESUMEN:

ComoresultadodelasmejorasenlatecnologíaLED(delinglés,light-emittingdiode),laspantallasdelamayoríadedispositivoselectrónicosactualesestániluminadasporLEDs.Muchassonlasventajasdeestafuentedeluzsobrelasfuentespredecesoras;sinembargo,algunasinvestigacionesrecienteshan puesto demanifiesto el hecho que la exposición prolongada a la emisión en la zona azul delespectro de los LEDs blancos puede tener un efecto negativo en la salud visual y en los ritmosbiológicos(ritmoscircadianos).Comoconsecuenciadeello, losfabricantesdelentesoftálmicashanintroducido recientemente en el mercado lentes innovadoras que incorporan filtros de luz azul,especialmentediseñadasparalosusuariosdedispositivoselectrónicos.Enestetrabajo,seevaluaronycompararondiferentesfiltrosdeluzazulenlentesoftálmicascomerciales.Sedisponíanlaslentesfrenteaunatabletaretro-iluminadaconLEDs,demanerasimilaracomounusuariosesituaríadelantedeldispositivoelectrónicoparaleeruntexto.Seanalizólacapacidaddeabsorcióndevariasmuestrasdeunmismofabricante,ysecomparóelresultadoentrefiltrosazulesdedistintasmarcascomerciales.Palabrasclave:Filtrosdeluzazul,lentesoftálmicas,pantallasretro-iluminadasporLED,

dispositivoselectrónicos,ritmocircadiano

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[12]C.Cajochen,S.Frey,D.Anders,J.Spati,M.Bues,A.Pross,R.Mager,A.Wirz-Justice,O.Stefani,"Eveningexposure toa light-emittingdiodes(LED)-backlitcomputerscreenaffectscircadianphysiologyandcognitiveperformance,"J.Appl.Physiol.,110,1432-1438(2011). https://doi.org/10.1152/japplphysiol.00165.2011

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[14]Reticare:http://www.reticare.com.DateofaccessDecember23rd2016.[15]J.Escofet,S.Bará,"Reducingthecircadianinputfromself-luminousdevicesusinghardwarefiltersand

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1.IntroductionInmodernsocietytheuseofelectronicdigitaldevicesisrapidlyincreasing,withcomputers,smartphones,tablets and televisions being ubiquitous. As a result, all age groups (children, youth and adults) reportincreasinglydemandingvisualtasks.Inaddition,particularresearcheffortsarebeingdirectedtoevaluatetherelationbetweentheuseofelectronicdisplaysandsomevisualproblems[1-3].Inparticular,in2008theAmericanOptometricAssociationdefinedtheComputerVisionSyndrome(CVS)asthecombinationofocular and vision problems initially associated with the use of computers [1-3], a definition that maynowadays be extrapolated to the use of any other type ofmodern electronic display. One of themost



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prevalentproblemsassociatedwithCVSisdryeye[4].Researchershavereportedthatoculardiscomfort,specificallydryeyesymptoms,maybeassociatedwithanincreaseofincompleteblinks(thatis,theeyeisnotcompletelyclosedinthedownwardprocessofablink)whenelectronicdisplaysareused[5].

Overall,oneofthemaincomponentsofelectronicdevicesisabacklightscreenconsistingofaliquidcrystaldisplay(LCD)layerandalightsource,whichissetbehindthescreen.Thisilluminationsystemallowstheuseofthesedevicesinpoorlylitenvironmentsand,ingeneral,improvesandfacilitatesvisualizationofdatashowninthescreen.Untilrecently,themostcommonlyusedbacklightsystemwasbasedoncoldcathodefluorescent light (CCFL). As a consequence of the recent improvement in light-emitting diode (LED)technology,thescreensofthevastmajorityofelectronicdevicesarenowilluminatedbywhitelightLEDs.TwoLEDconfigurationsareavailable: thoseemittingwhite light fromaphosphorouscoatingandthosecompounding white light by combining red, blue and green (RGB) LEDs. The advantages of the LEDtechnologyoverpreviousilluminationsystemsarenumerous,suchasaffordingawidervarietyofcolours,highercontrastandresolution,andthinnerscreens,amongothers.Nevertheless,somedisadvantageshavealsobeendescribed,whicharecurrentlystillunderstudy.Forexample,prolongedexpositiontothewhiteLEDsmainemissionintheblueareaofthevisiblespectrummayhaveanegativeimpactonvisualhealth,aswellas,onbiologicalrhythms(circadianrhythms)[6,7].Someofthenegativeeffectsofthisradiationmayoriginate in the coincidence of thewhite light LED emission peak (at approximately 450 nm)with thewavelength ofmaximum absorption of themelanopsin pigment of the retina (around 460 nm), whichregulatesthecycleofsleepingandwakinginhumanbiologicalrhythms(Fig.1).

Fig.1.SpectralradianceofaLEDbacklightscreen(inblack)andnormalizedspectralabsorptionvaluesofthemelanopsinpigment(in

blue)

Ithasbeenobservedthat,undernaturalconditions,thecircadiancycleoscillatesaccordingtolightexposure(specifically, light fromtheblueorshortwavelengthspectralregion).Atnight, indimlightordarkness,melatonin(orsleephormone)secretionbythepinealglandisinitiated,allowingthehumanbodytobecomereadytosleepandrest.Onthecontrary,duringtheday,melatoninsecretionisstoppedundertheexposureto sunlight, thus promoting a state of alertness and wakefulness. Nevertheless, this biorhythm cannotdifferentiateexposuretoanaturallightsourcefromthatofanartificiallight.Thereby,somestudieshavedocumented a disruptionof circadian rhythmswith theuse of electronic displays at night [8,9] and aninhibitionofmelatoninproductionbytheeffectofthebluelightemissionofLEDdisplays[10-13].

Inordertoreducetheleveloftheemittedbluelightreachingtheeyesofelectronicdisplayusers,differentapproacheshaverecentlybeenimplemented.Forinstance,asetoffilterswithdifferentattenuationlevelsiscommerciallyavailable[14].Thesefiltersaredesignedtobeattachedtothedisplays,sothattheypartiallyblockthebluelightemissionofthedevice.Anotherpossibilityistoinstallandactivateanapplicationforcomputers, smartphonesor tablets.This softwarewill automatically control theemissionof thedisplayaccordingtothetimeofthedaytheuserisemployingthedevice,movingtowardswarmercolourstowardstheendoftheday.Both,hardwarefiltersandsoftwareapplicationswererecentlycompared[15].Arecentworkhasinvestigatedtheuseororange-tintedblueblockertherapeuticlensestoreducetheeffectsofLEDilluminatedscreensoneveningusersofthesedevices[16].Finally,severalophthalmiclensmanufacturershaveintroducedinthemarketinnovativeophthalmiclensesincorporatingbluelightfilters.Theselenses



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arespecificallyrecommendedforordinaryusersofelectronicdevices,thusallowingprolongedexposuretothescreenradiation,orfornight-timeusers.

In this work, the performance of different blue light filters incorporated in commercially availableophthalmiclenseswastestedandcompared.Insection2,adetaileddescriptionofthematerialsusedfortheexperimentsaswellasthetestedsamplesisprovided.Section3focusesontheanalysisoftheobtainedresults, comparing the absorption capacity of various samples of the same manufacturer and alsocomparing various samples from four different ophthalmic lensmanufacturers. Finally, conclusions aresummarizedinSection4.

2.Materialandmethod2.a.ExperimentalsetupThecurrentstudyusedaniPadminiME280TY/AtabletfromAppleasanexampleofaself-luminousscreenwithLEDtechnology.TheilluminatingsystemconsistsofanarrayofRGBLEDsasshowninthemicroscopicviewofFig.2(a).Theareaofthistabletis20x13.47cmandwasusedastheilluminatinglightsourceforalltheexperimentalmeasurementsoftheophthalmiclensesunderstudy.Thetabletdisplayedauniformwhitepicturefillingthewholescreenin itsmaximumradianceandwasalwayspluggedtotheexternalpowersupplynetworktoensurethemaximumRGBLEDemission.Undertheseconditions, the initialemissionspectrum of the tablet was taken as a reference to lately compute the spectral transmission of theophthalmiclenses.Theradiometricmeasurementsinthisstudywereobtainedwiththespectroradiometer“PhotoResearchPR-715”,adevicethatallowsfortheanalysisofthevisiblespectrum(380-780nm)in4nmsteps(Figure3).Figure2(b)showstheexperimentallymeasuredspectralradianceofthetabletdisplayingawhiteuniformimageinitsmaximumradiance.

(a)(b)

Fig.2(a)MicroscopicviewoftheRGBLEDarrayoftheiPadminiME280TY/Atablet.(b)Spectralemissionofthesamedevice.

Fig.3Spectroradiometer(PhotoResearchPR-715)usedintheexperiments.

The analysed samples of ophthalmic lenseswere sequentially placed in front of the spectroradiometer,centred to the optical axis. The orientation effect of the lenses with reference to the display was firstconsidered.Preliminarymeasurementsevidencednovariation in thereadingsof thespectroradiometer



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irrespectiveoftheactualorientationofthelenses(concaveorconvexsurfacefacingthedisplay).Therefore,subsequent measurements were conducted with samples placed with the convex curvature facing thetablet,whichisthesameorientationauserwouldemploythelenseswhenreadingatextontheelectronicdevice.Thespectralradianceforeachlenswasrecordedandcomparedtothespectralemissionofthetabletscreenwithoutthelens.Therefore,anyvariationinthemeasuredspectralradiancewouldaccountfortheabsorptioncharacteristicsoftheanalysedophthalmiclens.Theratiobetweenthespectralradianceofthetablet with and without the lens provides the percentage of filter transmission for each analysedwavelength.Figure3showstheexperimentalsetup, includingthespectroradiometerusedtoobtain thespectral informationofthestudysamples.Allmeasurementsweretakenunderthesameenvironmentalconditionsandduringthesamesession.

2.b.AnalysedophthalmicsamplesNowadays,severalmanufacturersincorporatebluefiltersincommerciallyavailableophthalmiclenses.Thisstudyevaluatedsamples fromfourdifferentmanufacturers:Prats, Indo,HoyaandEssilor. Inallbutonecase,lenseswithbluefilterwerecomparedwithlensesincorporatingonlythecommonanti-reflective(AR)coating, with all the other parameters remaining constant (lens material, surface geometry, refractivepower,etc.).

Table1showsthenumberofevaluatedsamplesasgroupedbymanufacturer.TherewasonlyonesamplefromHoya,correspondingtothebluefilter,thatis,thelenswithARcoatingwasnotavailableintimeforthestudy.However,theauthorsconsideredinterestingtoincludethissampleintheanalysistoallowforcomparisonwiththeotherlensesincorporatingblueradiationfilters.Incontrast,therewere4differentsamplesfromPrats:onewiththeARcoating,onewiththebluefilterforelectronicdeviceusers(CSR)andtwomoresamplesdefinedastherapeuticlenses,withfiltersCSRaandCSRb.

Table1.Numberofsamplesforeachoftheanalysedlenseswithinformationontheintensityofthebluefilter.Brand Total

numberofsamples

Sampleswithonlyanti-reflective(AR)

coating

Sampleswithbluefilter(intensityoffilter)

Prats® 4 1-AR 3-CSR;CSRa;CSRbIndo® 2 1-AR 1-EnergyHoya® 1 0 1-BlueControlEssilor® 2 1-AR 1-CrizalPrevencia

Figure4showstheanalysedophthalmiclenssamplesincorporatingbluefilter.Acertainyellowishcolourmaybeobservedfromsomeofthesamplessincelenseshaveaselectiveabsorptioninthebluecomponentofthevisiblespectrum.

(a)

(b)

(c)

(d) (e) (f)Fig.4.Samplesoftheanalysedophthalmiclensesincorporatingabluefilter:(a)CSR,(b)CSRa,(c)CSRbfromPrats;(d)Energyfrom

Indo;(e)BlueControlfromHoya;(f)CrizalPrevenciafromEssilor.



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3.ResultsIn this section, the spectral radiances and transmittances of the samples belonging to the samemanufacturer are shown and compared. In all cases, the tablet spectral radiance is also plotted forcomparisonpurposes.

Figure5showsthespectralradiancesandtransmittancescorrespondingtothePratsophthalmiclenses.ItmaybeobservedthattheARcoatingrarelyabsorbedlightfromanywavelengthofthevisiblespectrum,witharadiancecurveclearlyoverlappingtheemissioncurveoftheiPadtablet.Onthecontrary,thethreeCSRfiltersampleseachmodifiedinadifferentdegreetheevaluatedspectrum.TheCSRsampledesignedforelectronicdeviceusersspecificallyabsorbedtheblueregionofthespectrum,wheretheRGBLEDsemissionhasthehighestintensity.TheCSRaandCSRbsamples,however,modifiedthewholeofthevisiblespectrum,manifesting a significant absorption in all chromatic components,with the strongest effect in the shortwavelengths. Note that these therapeutic lenses are commonly recommended to avoid dazzle in thosepatientswithlightsensitiveretinas.

Fig.5.SpectralradiancesandtransmittancesobtainedfromthesetofophthalmiclensesfromPrats.Thecurveofthetabletscreen

emissionisshownforcomparison.

Figure6depictstheresults fortheIndoophthalmic lenses.Hardlynoticeabledifferences inthespectralradiancesmeasuredfromthetabletscreen,theARcoatingandtheenergyfilterwereevidenced,althoughatinyreductionoftheradianceintheblueregionofthespectrummaybeappreciatedwiththebluelightfilter.ThiseffectcanbeclearlyobservedinthetransmittanceplotontherightofFigure6.

Fig.6.SpectralradiancesandtransmittancesobtainedfromthesetofophthalmiclensesfromIndo.Thecurveofthetabletscreen


ThecurvesfortheBlueControlsampleofHoyaareplottedinFigure7.ThislensisdirectlycomparedwiththeemissionofthetabletsincetheARcoatingsamplewasnotavailable intimeforthestudy.ItmaybeobservedfromFig.7thattheHoyalensselectivelyabsorbedonlyintheblueregionofthevisiblespectrum,



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thatis,itreducedslightlythemaximumemissionpeakofthetabletintheshortwavelengtharea.Alltheotherwavelengthsinthevisiblespectrumremainedunaltered.

Fig.7.SpectralradiancesandtransmittanceobtainedfromtheophthalmiclenswithBlueControlfilterfromHoya.Thecurveofthe

tabletscreenemissionisshownforcomparison.

Finally,theresultsfromtheEssilorsamplesarepresentedinFig.8.TheradianceandtransmittancecurvesevidencethattheARcoatingofEssilordidnotaffectthespectralinformationoftheilluminatinglightsource(tabletwhitescreen).Onthecontrary,theCrizalPrevenciabluefilterreducedaportionoftheblueemissionof the RGB LED screen. The other wavelengths of the visible spectrum remained unaltered with theincorporationofthebluefilter.

Fig.8.SpectralradiancesandtransmittancesobtainedfromthesetofophtthalmiclensesfromEssilor.Thecurveofthetabletscreen


Fig.9.Spectralradiancesandtransmittancesobtainedfromthesetofophthalmiclensesincorporatingbluefilters.Thecurveofthe

tabletscreenemissionisshownforcomparison.



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Toallowforabettercomparisonbetweenbluefilters,Fig.9depictsthemeasuredspectralradianceandtransmittanceofthetabletwhentheophthalmiclensesincorporatingbluefiltersforelectronicdeviceusersaresequentiallyplacedinfrontofthescreen.Itmaybenoticedthatalltestedlensesincorporatingabluefilter performed a selective absorption in the blue region while transmitting the energy of the otherwavelengthsofthevisiblespectrum.

Table2summarizestheobtainedexperimentalresultsintermsofthepercentageofabsorbedlightatthemaximumemissionpeakoftheRGBLEDself-luminoustabletforeachophthalmiclenswithbluefilter.

Table2.Percentageofabsorptionatthemaximumtabletemissionpeakforthetestedophthalmiclenseswithbluefilter.

Lenses Absorption(%)Prats(CSR) 14.7%Indo(Energy) 2.9%

Hoya(BlueControl) 7.1%Essilor(CrizalPrevencia) 17.4%

ItmaybenotedfromTable2thatthepercentageofbluelightfilterabsorptionvariedsignificantlybetweenmanufacturers,witharangefrom3%ofabsorptionfortheIndoEnergysampleto17.4%fortheEssilorCrizalPrevencialens.TheBlueControlfromHoyaandtheCSRfromPratsprovidedintermediatevaluesofabsorption, with a 7.1% and a 14.7%, respectively. It is also interesting to remark that the degree ofabsorptionofeachlenscoincidedwiththecorrespondingyellowishperceptionshowninFig.4.Thus,Figure4(f)and4(a)correspondtothehighestbluelightabsorptionoftheEssilorandPratssamples,whileFigure4(e)and4(d)arethemostlytransparentlensesfromHoyaandIndo.

4.ConclusionsInthisstudy,theauthorsanalysedseveralsamplesofophthalmiclensesthatincorporatebluelightfilters,specificallydesignedforelectronicdeviceusers.Asadvertisedbythemanufacturers,theselensesaresoldtopreventvisualfatigueandocularpathologies.Toachievethisaim,theincorporatedfilterspartiallyblockthebluelightemissionofLEDilluminatingsourcesusedintabletsandotherelectronicdevices.

This study has firstly confirmed that a self-luminous iPadminiME280TY/A (Apple tablet) presents anemissionpeakintheblueregionofthevisiblespectrum,withamaximumradiancearound450nm.

Secondly,whenplacingARcoatingophthalmiclensesinfrontoftheRGBLEDilluminatedtablet,thespectralradiance of the system remained unaltered for all the evaluated samples obtained from differentmanufacturers:Prats,IndoandEssilor.

Thirdly,ophthalmiclensesincludingbluefiltersforelectronicdeviceuserswerefoundtoalterthespectralradianceofthetabletonlyintheblueregionofthevisiblespectrum,specificallyatitspeakofmaximumemission.Therefore,itmaybeconcludedthatcommerciallyavailablebluefiltersinophthalmiclensesareeffectivetoabsorbsomeoftheshortwavelengthemission.Nevertheless,eachcommercialfiltershowsadifferentdegreeofbluelightattenuation.Therangeofabsorptionamongthefourtestedbrandsoflensesgoesfrom3%fortheIndosampleto17.4%fortheEssilorsample.Additionally,itisrelevanttonotethatlenseswiththehighestyellowishappearancecorrespondtothosewiththehighestlevelofabsorbanceofthebluetabletemission.

Thepresentfindingsrevealingawiderangeofbluelightattenuationincommerciallyavailablebluefilterssupporttheneedtoaccuratelydeterminethebluelightabsorptionlevelrequiredtoavoidpossibleocularpathologiesandfluctuationsinthecircadianrhythm.

Acknowledgements

AuthorswouldliketothanktheMinisteriodeEconomíayCompetitividad(Spain)andFEDERfundsforfinancialsupport(projectDPI2013-43220-R).

type: research paper section: vision sciences spectral ... · como consecuencia de ello, los...

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