Realization of a radiometric head for measurements of ultraviolet total erythemal effective...

Realization of a radiometric head for measurements ofultraviolet total erythemal effective irradiance

Maria-Guglielmina Pelizzo,* Denis Garoli, and Piergiorgio NicolosiDepartment of Information Engineering, CNR-INFM LUXOR, University of Padova, via Gradenigo,

6B-35131 Padova, Italy

*Corresponding author: [email protected]

Received 20 October 2006; revised 10 April 2007; accepted 10 April 2007;posted 10 April 2007 (Doc. ID 76311); published 6 July 2007

An innovative sensor with a spectral response equivalent to the erythemal action curve for ultraviolettotal effective irradiance measurements is presented. Optical and sensor components have been selectedafter the characterization of different samples. The design is based on an innovative interferential filter,which has been realized and tested. A first prototype has been assembled and characterized. Ourmeasurements demonstrate the feasibility and potential of this instrument. © 2007 Optical Society ofAmerica

OCIS codes: 120.4640, 040.7190, 350.2460.

1. Introduction

The ultraviolet (UV) spectral region actually refersto three ranges of light: UV-A �315–400 nm�, UV-B�280–315 nm�, and UV-C �100–280 nm�. On Earththe more energetic UV-C rays are absorbed by atmo-spheric oxygen and do not reach the soil, while UV-Brays are only partially absorbed in the ozone layer,and UV-A rays fully penetrate the atmosphere.

UV radiation overexposure is related to severalphotobiological reactions, such as eye and skin dam-age and DNA mutations [1]. Chronic and acute expo-sure to UV radiation increases the risk of developingnonmelanoma skin cancer; Ref. 2 reports the associ-ation between UV exposure and malignant mela-noma. UV radiation not only causes skin aging, it canalso trigger or exacerbate many diseases such as pho-totoxic or photoallergic reactions and autoimmunediseases [3]. The large increase in the incidence ofskin cancer may be caused by the reduction of UVabsorption in the atmosphere [4] owing to ozone de-pletion. Other scientific studies demonstrate that thefashion of intermittent exposure to UV radiation in asolarium could also be a cause of melanoma cancerdiffusion increase [5]. Many countries and laborato-

ries have set up observatory stations for monitoringUV irradiance associated with Sun rays striking theEarth’s surface; as a consequence ultraviolet relatedinstrumentation have gained increasing attention[6,7]. On the other hand, UV rays are fundamentalfor synthesizing vitamin D [8]. UV radiation can beuseful in many medical applications: for example,psoriasis and dermatitis are commonly cured by ir-radiating the damaged skin area with UV radiation[9], while disinfection of tools can be accomplished bythe use of UV sterilizers. Moreover UV lamps in suntanning centers are largely used for aesthetic pur-poses.

The wide use of UV radiation for therapeutic,aesthetic and, germicidal purposes has led to anincreasing demand for UV sensors. Broadband UVradiometers and spectroradiometers are the instru-ments used to determine the total irradiance or thespectral irradiance (i.e., irradiance as function of thewavelength), respectively [10]. For any specific appli-cation, the choice of the proper instrument is funda-mental. Some radiometers, for example, are designedto have a spectral response that matches an actioncurve, which describes the relative effectiveness ofUV radiation at a particular wavelength in producinga particular biological response; in such a way, verycompact and efficient instruments can be realized. Anaction curve for a given biological effect is used as a

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1 August 2007 � Vol. 46, No. 22 � APPLIED OPTICS 4977

wavelength-dependent weighing factor relative to thespectral UV irradiance (180–400 nm). The actualbiologically effective irradiance �Weff�m2� is then ob-tained by integrating the weighed spectral irradianceover the wavelength. The effective UV dose (in J�m2)is found by integrating the effective irradiance overthe exposure period.

The erythemal action curve (EAC) (or erythemalaction spectrum), defined by McKinlay and Diffey,has been accepted by the Commission Internationalede l’Eclairage (CIE) as the standard representation ofthe average skin response to UV-B and UV-A (Fig. 1)[11]. In the European regulation EN60335-2-27 thehazard of UV radiation emitting machines for domes-tic use is discussed, and upper-limit effective expo-sure doses are established according to the CIE EACdamage [12].

Different devices with a spectral response closeto the erythemal action spectrum have been designedand commercialized. Many are based on theRobertson–Berger design [13,14] (for example, theone produced by Solar Light Co., Glenside, Penn.,USA), that consists of a GaAsP diode and a combina-tion of absorption filters and a phosphor, and whichconverts the UV radiation into green visible light.This instrument represents a standard for outdoorapplications, and it is largely used in meteorologicalstations. However compliance with the erythemal ac-tion spectrum can be considered poor for some appli-cations [15], as in the case of irradiance measurementof UV-A solar lamps used in tanning units, whichmainly emit in the 320–400 nm, or of lamps emittingbelow 280 nm. Moreover, the response of Robertson–Berger devices can be affected by temperature varia-tions so that correction or stabilization is needed [16].Other instruments are based on the use of UV visible-blind photodiodes, which have recently become avail-able on the market. For example, Solartech Inc.Harrison, Mich., USA, offers an instrument based on aSiC photodiode coupled with a glass filter; while DavisInstruments Corp. Hayward, Calif., USA, adopts a de-sign where radiation, filtered by a hard-oxide multi-layer coating, is detected by a UV photodiode. Otherimportant European producers are Kipp and ZonenDelft, the Netherlands, and Gigahertz-Optik, Puch-heim, Germany. Finally, AlGaN Schottky photodiodesfor solar UV monitoring have been developed [17,18];

the performance of this kind of detector has been eval-uated in this work (see Subsection 2.B).

To measure the total effective irradiance of solarUV and artificial sun lamps [19], an innovative handportable radiometer with a spectral response curveequivalent to the CIE erythemal action spectrum hasbeen designed and realized. The sensor has been pat-ented in Italy and the international extension of thepatent has been requested [20]. Its concept is basedon the realization of an innovative multilayer filtercoupled with a SiC photodiode.

Due to the filter properties, the sensor shows su-perior performance by very accurately matching theEAC. In particular, theoretical calculations showthat the fitting of the erythemal action spectrum pro-vided by this instrument is, to the best of our knowl-edge, much better than that of any other commercialsolutions. A first prototype to prove its superior spec-tral performance has been assembled and tested.

2. Instrument Design, Components, and PerformancesEvaluation

A. Instrument Layout

A picture of the instrument is shown in Fig. 2. Theinstrument display output is the total UV erythemaleffective irradiance, Weff�m2, which corresponded tothe action curve weighed irradiance. A handy devicewas realized by connecting the sensor head to theinstrument via a cable of �0.5 m length. As shown inFig. 3 the instrument design layout consisted of atransmission diffuser, an interferential filter, and aphotodiode detector. The sensor head entrance opticswas a Lambertian diffuser, i.e., the equivalent en-trance aperture varied with the radiation incidenceangle according to cosine law. A low cost but reliablecommercial photodiode was used as a detector. Boththe diffuser and the photodiode were selected to beeasily procured. To match the EAC, the filter was de-signed to compensate for the photodiode and diffuserspectral response according to the following equation:

CIE EAC��Rph�� Rdiff��

� Rfilter��, (1)

where the CIE EAC (�) curve is reported in Fig. 1,Rph�� is the photodiode spectral response, Rdiff�� is

Fig. 2. Picture of the realized prototype.

Fig. 1. CIE EAC.

4978 APPLIED OPTICS � Vol. 46, No. 22 � 1 August 2007

the diffuser transmission, and Rfilter�� is the filtertransmission.

An analysis of commercially available photodiodesand diffusers was performed to choose the most ap-propriate component and to recover the Rdiff�� andRph�� curves. Then a completely new filter with atransmission curve matching the nominal Rfilter��spectral efficacy curve was designed, realized, andtested. An instrument prototype model was assem-bled, and calibrated. A description of all these tech-nical aspects will be presented next.

B. Photodiode

To choose the most appropriate sensor, different UVphotodiodes were considered. They were all blind inthe visible and IR, to prevent out-band radiationleakages. The considered samples were:

Y SiC photodiodes, nominal area 0.22 mm2 (num-ber of samples: 6),

Y p-i-n GaN photodiodes, nominal area 0.5 mm2

(number of samples: 2), andY Different AlGaN Schottky photodiodes, nomi-

nal area 0.5 mm2: (A) with peak response at 250 nm(number of samples: 2), (B) with peak response at300 nm (number of samples: 2), and (C) with peakresponse at 300 nm � UV filter window to cut-offvisible light (number of samples: 2).

Both their relative (Fig. 4) and absolute spectralresponses (Fig. 5) were measured. A technical de-scription of facilities and method used is reportedelsewhere [21]. AlGaNs and GaNs seem to have alower sensitivity with respect to SiC, therefore largeractive area detectors would be necessary to get sim-ilar efficiency levels with a significant cost impact.

AlGaNs with 300 nm cutoff are usually sold for thematching between their spectral response and theEAC [18]. Unfortunately our sample did not perform

as expected; in fact, the fitting of EAC was evaluatedto be worse than that of other commercial devices.Since GaNs are not sensitive enough above 360 nmthey are not suitable to cover the whole relevantwavelength range �250–400 nm�. On the contrary theSiC photodiode had the highest absolute spectral re-sponse in almost the whole spectral range; all sixsamples showed equivalent responses. Furthermore,they are quite stable for high temperature values.Due to the high value of their shunt resistance theycan measure even small current values. Finally, theyare easily available on the market. As such the SiCphotodiode was selected as the most suitable detectorcomponent for the final device realization. Thereforethe Rph�� values to be used in Eq. (1) are those re-lated to a SiC photodiode (actually, a rescale by aconstant value is possible, since only the relativeshape of the response is of interest).

C. Diffuser

Diffusers in the UV spectral range are typically real-ized in Teflon or quartz. In this project different sam-ples were characterized:

Y Laboratory prepared quartz with a thickness of1.9 mm, and suprasil with a thickness of 2 mm,

Y Teflon AF1600 from Dupont,Y Zenith SG 3201 with a thickness of 0.1 mm,

from Oriel, andY Different laboratory prepared Teflon samples

with thicknesses of 0.3, 0.5, and 1 mm.

Transmission to determine Rdiff��, and Lamber-tian diffusion properties of the samples, were tested.Direct transmission measurements were performedat Delta Ohm s.r.l., Caselle di Selvazzano, Padova,Italy, using a Bentham f�4 double spectral monochro-mator equipped with a halogen tungsten lamp (for� � 300 nm) and a deuterium lamp (for � � 300 nm).The same system was used for the measurement ofthe photodiode’s relative spectral response, and itsdescription is reported elsewhere [21]. A spectral in-tensity scan of the beam with and without the dif-fuser sample inserted in the optical path wasacquired by a Si calibrated photodiode, and transmis-sion was obtained by the ratio of the two spectra.Some results are reported in Fig. 6 as an example.

Diffusion property measurements were conductedby using the experimental apparatus reported in Fig.

Fig. 3. Layout of the radiometer.

Fig. 4. Relative spectral response curve of different photo-diodes.

Fig. 5. Absolute spectral response curve of different photo-diodes.


7. A Xe–Hg 1000 W lamp was used as a source. Thebeam was collimated by a set of lenses. The samplewas placed inside a case mounted on a rotation stagewas to vary the beam incidence angle. An optical fiberrigidly connected to the case at 2 mm distance fromthe rear face of the diffuser plate collected the trans-mitted beam. The rotation stage was placed on athree-axis translation stage to facilitate initial sam-ple alignment. The alignment was accomplished byusing a He–Ne laser beam to set the rotation axisvertical—intersecting the optical axis of the appara-tus on the front surface of the diffuser. The transmit-ted intensity was recorded at steps of 5°. The opticalfiber was connected to an Ocean Optics USB2000spectrometer, that separates the different spectralcomponents. In this way diffusion properties wererecovered at wavelengths corresponding to differentemission lines of the Hg spectrum. For each spectralline, the transmitted intensity curve versus the angleof incidence was calculated by normalizing eachvalue at the 0° angle intensity one. As an example,diffusion properties derived at 366 nm are reportedin Fig. 8 for different samples. The best diffuser wasTeflon, which matched the cosine curve very well inthe whole range. However, if the thickness of theTeflon is �1 mm, its regular transmission is low(around 5%), which can be a problem in detectingirradiance of low power sources, unless larger areaphotodiodes are used to compensate for power losses(with additional cost). Although thin Teflon diffusers,such as SG3021, have high transmission (50%), theyare difficult to mount and support in the instrumentcase. Therefore, owing to budget limits, for this pro-totype a laboratory prepared quartz diffuser wasused, since quartz has a high enough transmission to

allow the use of a low cost, small, and active areaphotodiode. If better diffusion properties are needed,the instrument can be realized with another Teflondiffuser. In this case a larger active area photodiodecan be adopted if small signals need to be measured.For this prototype the Rdiff�� in Eq. (1) is the quartzsample reported in Fig. 6. Consequently this firstprototype only provided accurate measurements forquasi-collimated radiation while maintaining supe-rior spectral performance.

D. Filter Design, Deposition, and Characterization

The nominal interferential filter curve, Rfilter�� (re-ferred to as “the target curve”) was derived, accordingto Eq. (1), from the ratio between the nominal EACand the product between the photodiode spectral re-sponse curve Rph and the quartz spectral transmis-sion Rdiff. Figure 9 shows the transmission targetcurve obtained by setting its maximum value at100%, which maximized the signal on the photodiode.

Commercial software (TFCALC–Software SpectraInc.) was used to optimize the design of the filter thatcan simulate the optical properties of film structuresconsisting of �5,000 layers deposited on the front oron the back surface of a suitable substrate. An opticalconstants database, both for substrates and film ma-terials, can be stored in the form of tables or complexrefractive index dispersion formula versus wave-lengths. The materials database, available free ofcharge for research purposes by Sopra Company(http://www.sopra-sa.com/more/database.asp), was usedfor first theoretical calculations; however, the opticalconstants used for the final design of the filter wereexperimentally derived (see Section 3). Different il-

Fig. 6. Regular transmission of some diffuser samples.

Fig. 7. Sketch of the setup used for the measurement of thediffuser properties of different samples.

Fig. 8. Diffusion properties of some samples measured at 366 nmwavelength.

Fig. 9. Filter target curve and filter designed transmission.


luminants stored in a database as tables of spec-tral intensity versus wavelength can be used toevaluate the performance of the optical element. Inthis case, the spectral intensity distribution corre-sponding to the white illuminant was alwaysadopted. The radiation incident on the film can be acollimated beam or a cone of rays with a given angu-lar aperture, and the angle of incidence can be variedfrom 0° to 89.999°. In the case of a cone of rays, thecomputed transmission corresponds to the averagevalue for the considered angular beam aperture.

The software follows an optimization procedure toobtain a filter structure with a transmission curvethat matches the “target curve” as closely as possible(in this case the Rfilter(�) curve). Different materialcouples and numbers of layers were considered in thedesign. By using the optimization software tools, thethickness of each single layer was calculated to min-imize the difference—set according to a merit func-tion between the target curve and the transmissioncurve of the filter under design. In Fig. 9 the trans-mission of an optimized filter with a structure madeof standard materials SiO2�ZrO2 is compared withthe structure derived by using 32 alternate layers ofMgF2 and ZrO2. The improved matching of the EACtarget curve obtained with the new design is clear.(We are not aware of the realization of an interferen-tial filter based on this material couple made with somany layers.) The substrate is UV grade fused silicawith a thickness of 1 mm.

The spectral response of the detector head, derivedfrom the product of the characteristic curves of thedesigned filter, the SiC photodiode, and the diffuser,have been compared with the EAC (Fig. 10). It is clearfrom Fig. 10 that the match between the curves isvery good for a collimated radiation that has an inci-dence angle of 0°. Since the spectral response of theinterferential filter depends on the radiation inci-dence angle on the filter, by using the specific TFCalctool previously described, the sensor response for dif-ferent cone angles was also simulated. The match ofthe EAC was excellent in the case of a 40° incidenceradiation cone angle (Fig. 10); this means that thedetector head design should define the field of viewangular aperture of the SiC photodiode within thisvalue, i.e., the distance between photodiode and the

entrance optics must be set accordingly. (This anglemust not be mixed up with the input angle: radiationcoming from the whole 180° solid angle in space im-pinges the diffusing entrance optics.)

Test filter samples were developed by Luxel Cor-poration Inc. Preliminary work on material charac-terization was performed to recover the opticalconstants of ZrO2 and MgF2. The experimentally de-rived optical constants are reported in Fig. 11 to-gether with those available from the Sopra database.The differences can be attributed to different deposi-tion process techniques. The final design of the filter(Fig. 9) was optimized by using the experimentallyderived optical constant data. Luxel realized threeidentical filters: 799-1,-2, and -3. The transmissionmeasurements of filter 799-1 are reported in Fig. 12together with the target curve for comparison. Mea-surements were carried on at Delta Ohm by using theBentham double spectral monochromator, and dataare completely in agreement with the results ob-tained independently by Luxel. Analogue resultswere obtained more recently in our laboratory by us-ing the Varian Cary 5000 spectrophotometer. Fromthe data results reported in log scale it was clear thatthe filter manufacturing tolerances mainly affectedlow transmission values, while the short wavelengthedge of the filter transmission curve was quite wellreproduced. We are confident that we can obtain bet-ter performance with a slight improvement in thedeposition procedure. Measurements were extendedto the visible region to better understand the struc-ture of the filter. The analogue results were found forfilters 799-2 and 799-3. Filter transmission was wellin agreement with the nominal target curve. The fil-

Fig. 10. Theoretical spectral response performances of the wholesensor compared with the EAC.

Fig. 11. Optical constants of filter materials.

Fig. 12. Filter target curve, designed filter theoretical transmis-sion curve and experimental one.


ters showed the same transmission curve, whichmeans that they were stable in a relatively shortperiod of time after deposition and that the filterswere reproducible during same deposition session.The uniformity of the filter was tested by varying thesize and position of the tested area.

To verify stability filter 799-2 was subjected tothermal cycling. In the first cycle the temperaturewas increased from 25° to 80° in �1 h. The filter wasmaintained at that temperature for another hour andthen cooled down in 14 h. During the second cycle, thesample was maintained at 80° for 2 days, and thencooled down in 0.5 h. After the thermal treatment,the characteristic of the filter was measured again,showing unchanged performance. The same filterwas measured 1 year after deposition, again showingthe same transmission curve. Recently, filter sample799-1 was exposed to unfiltered UV visible IR radia-tion from an Oriel solar simulator equipped with a300 W xenon lamp. Four irradiation sessions wereorganized in four consecutive days. During each ses-sion the filter was irradiated with a total of 200 Stan-dard Erythemal Dose. After each session, the filtertransmission was measured with the Varian Cary5000 spectrophotometer. No systematic variation ofthe transmission curve with total accumulated dosewas observed. The maximum relative difference be-tween single data points related to two differenttransmission curves was 0.06%, which is well withinstatistical tolerances. These very preliminary exper-iments of stability versus solar radiation exposurewere encouraging and further studies and test ses-sions are planned.

E. Prototype Realization

All sensor components were assembled in a blackplastic case, with a diffuser as the input optics. Therelative spectral response of the system was mea-sured by the use of the f�4 Bentham double spectralmonochromator equipped with 1800 lines�mm grat-ings and halogen–tungsten (for � � 300 nm) and deu-terium lamp (for � � 300 nm) sources. Measurementswere performed at 2 nm steps with 2 nm spectralbandwidth. The results were compared with the onesexpected according to the measured characteristics ofeach single component. The output photodiode cur-rent was amplified by a current�voltage amplifiermounted on a proximity circuit inside the radiometerhead. Besides the amplifying function, the circuit al-lowed the measurement of the photocurrent in fourdifferent scales automatically selected to avoid satu-ration. The radiometer head was connected to an in-dicator by a cable (Fig. 2). Inside the indicator therewas also another amplifier. Two trimmers allowedthe setting of the instrument zero and sensibility. Onthe display the total effective irradiance value�Weff�m2� was observed.

To determine the absolute spectral response ofthe radiometric head calibration was performed at254 nm. The absolute response at other wavelengthswas recovered by rescaling the previously obtained

relative spectral response curve. The Bentham in-strument collected the radiation emitted by a set oflow pressure mercury lamps and filtered by an inter-ferential filter centered at a 254 nm. In this way veryhigh spectral purity was obtained. A lens system wasplaced after the exit slit to collimate the beam. Asilicon photodiode calibrated at National PhysicsLaboratory (NPL, UK) was used as the standard ref-erence. Absolute calibration was obtained by a com-parison between measurements performed with thetwo detectors, i.e., the reference photodiode and pro-totype radiometric head. Calibration errors wereestimated to be lower than 10%. The normalized spec-tral response of the radiometric head is reported inFig. 13 together with the theoretical expected and theEAC for comparison.

3. Discussion

Due to the poor quality of the diffuser measurementswith this prototype were only accurate for collimatedspectral radiation. Nevertheless, much better perfor-mance could be obtained if the quartz was replaced byTeflon. According to the document “UVNET WG1:Guidance for UV power meter classification for par-ticular applications” [22], wherein a standard methodto fully characterize a UV meter by the use of 11parameters was proposed, the directional character-istic of a radiometer is expressed by a parametercalled f2, which must be experimentally evaluated. Inthis case we have estimated f2 � 0.65 in the case ofa quartz diffuser, and f2 � 0.065 in the case of aTeflon diffuser. These values were calculated fromexperimental data on diffuser properties using theproposed formula.

The response linearity of the sensor can be derivedthrough the characterization performed on photo-diodes [23] since the other components do not affectthis property. The linearity of the detectors was eval-uated by using different setups. For the linearity athigh intensity two lamps—a 300 W Xe and a 1000 WXe–Hg—were used. The intensity of the Xe–Hg lampwas varied; moreover, the photodiode was exposed toonly one or both sources by using a shutter system.Detector output signals were registered, and it wasverified that photocurrent values in the case of simul-taneous exposure to both lamps correspond to the

Fig. 13. Measured spectral response of the prototype calibratedat 254 nm.


sum of the values acquired with each source. Themaximum deviation from the linearity was found tobe 3.5% for an output total signal of some �A. Thesame approach was used to verify the linearity for alow intensity signal; in this case two halogen lampswere used and the maximum deviation was found tobe 3.2% for an output total signal of 90 pA. The op-erating range of the sensor was between a fewmW�m2 and 100 W�m2.

Although dedicated measurements were been per-formed, we concluded that the detector head responsewas not critically dependent on temperature varia-tions. This conclusion was based on the characteristicof its components: diffuser, filter, and detector, withonly some possible limitation about Teflon stability.This behavior was different from detectors based onphosphor conversion since their efficiency was tem-perature dependent.

“Fatigue” of an instrument is the reversible tem-poral change of its response, under constant operat-ing conditions, caused by incident irradiance. In thiswork fatigue was measured according to the methodproposed by Thematic Network for Ultraviolet Mea-surements [22]. A Lot-Oriel 300 W full spectrum solarsimulator that ensures a well stabilized irradiationwas used to irradiate the radiometer. The instrumentwas previously kept unexposed to radiation for 1week. The fatigue parameter f5 was evaluated to be0.035 after 30 min of exposure.

While the radiometer spectral response theoreti-cally matched the EAC very closely, the prototypecurve deviated from the target owing to the fact thatthe filter transmission was not the nominal one. Inorder to evaluate prototype performance, the appli-cation to a sunbed lamp’s irradiance measurementwas considered. The spectra of different lamps mea-sured by the use of the Bentham double spectralmonochromator have been taken into account (someare reported in Fig. 14). To perform these measure-ments, an integrating sphere (10 mm circular aper-ture) was used as the entrance optics of the systemand placed in different positions inside the sunbeds.The detector was a photomultiplier tube with a bial-kali photocathode. Measurements were performed byusing the 1800 line�mm grating, at step of 1 nm,with a spectral bandwidth of 1.8 nm. The sunbed

irradiance values were obtained by a comparison to adeuterium lamp calibrated at NPL and used as thereference source. The total effective irradiance of sev-eral lamps was derived by using both the EAC andthe absolute spectral response of the prototype. Themean value of all Weff�m2 values calculated in the twocases was derived, and a correction factor C to beapplied to the radiometer output was found accordingto the following relation:

Average��Weff�m2�CIE� � C � Average��Weff�m2�PROT�.

The Weff�m2 values related to the spectra of the lampsin Fig. 14 were calculated by using both the EAC andthe absolute spectral response corrected by the Cfactor. The results are reported in Table 1 for com-parison together with the percentage difference,which was used to represent the error of the proto-type for each single measure. As can be seen in Table1 the mismatch of the data derived by using the CIEnominal EAC and those provided by the instrumentwere on the order of a few percent. Preliminary testsin real sun tanning units were also performed, allow-ing the determination of the total effective irradiancereceived by a subject on different body parts.

4. Conclusions

A new, to the best of our knowledge, patented porta-ble UV radiometer sensor with a spectral responseequivalent to the EAC was presented. By using inno-vative filter optics, the theoretical response of theinstrument showed superior spectral performance,very accurately matching the EAC. The first proto-type was successfully realized, showing very goodpreliminary spectral performance, which can be fur-ther improved by optimizing the filter deposition pro-cess. The prototype estimated error in measuringsunbed irradiances was of a few percent with respectto the values expected according to the EAC. Theinstrument is hand portable and user friendly, andcan also be used for personal purposes. Besides adescription of the sensor this paper also containsvaluable technical information regarding optical andsensor parts useful for the development of UV instru-mentation.

The authors thank P. Ceccherini and P. Masut ofDelta Ohm s.r.l.-Caselle di Selvazzano, Padova, Italyfor all discussions and fundamental technical sup-port, David Grove of Luxel Corporation for making

Fig. 14. Some sunbed lamps spectra, effective spectra and totaleffective irradiance values.

Table 1. Total Effective Irradiance for Lamps of Fig. 13 Calculated bythe Use of the Nominal EAC and, for Comparison, the Prototype

Spectral Response

Weff�m2 EAC Weff�m2 PrototypePercentage Error

(%)

1.17 1.08 70.10 0.09 100.47 0.52 90.58 0.59 2


the filters, and Silvia Cella for her consultation re-lated to the intellectual property aspects of thepatent. This work was supported under INFM grant“Progetto Ponte 2002”.

References1. R. P. Gallagher and T. K. Lee, “Adverse effects of ultraviolet

radiation: a brief review,” Prog. Biophys. Mol. Biol. 92, 119–131 (2006).

2. G. B. Ivry, C. A. Ogle, and E. K. Shim, “Role of sun exposure inmelanoma,” Dermatol Surg. 32, 481–492 (2006).

3. P. McLoone, G. M. Woods, and M. Norval, “Decrease in Lang-erhans cells and increase in lymph node dendritic cells follow-ing chronic exposure of mice to suberythemal doses of solarsimulated radiation,” Photochem. Photobiol. 81, 1168–1173(2005).

4. B. L. Diffey, “Stratospheric ozone depletion and the risk ofnon-melanoma skin cancer in a British population,” Phys.Med. Biol. 37, 2267–2279 (1992).

5. P. Autier, “Perspective in melanoma prevention: the case ofsunbeds,” Eur. J. Cancer 40, 2367–2376 (2004).

6. B. Petkov, V. Vitale, C. Tomasi, U. Bonafé, S. Scaglione, D.Flori, R. Santaguida, M. Gausa, G. Hansen, and T. Colombo,“Narrowband filter radiometer for ground-based measure-ments of global ultraviolet solar irradiance and total ozone,”Appl. Opt. 45, 4383–4395 (2006).

7. T. Ingold, C. Mätzler, C. Wehrli, A. Heimo, N. Kämpfer, and R.Philipona, “Ozone column density determination from directirradiance measurements in the ultraviolet performed by afour-channel precision filter radiometer,” Appl. Opt. 40, 1989–2003 (2001).

8. P. Lips, “Vitamin D physiology,” Prog. Biophys. Mol. Biol. 92,4–8 (2006).

9. C. Green, B. L. Diffey, and J. L. M. Hawk, “Ultraviolet radia-tion in the treatment of skin disease,” Phys. Med. Biol. 37, 1–20(1992).

10. B. L. Diffey, “Sources and measurement of ultraviolet radia-tion,” Methods 28, 4–13 (2002).

11. CIE (International Commission on Illumination) Research

Note 1987, “A reference action spectrum for the ultravioletinduced erythema in human skin,” CIE J. 6, 17–22 (1987).

12. European regulation EN 60335-2-27, 1997-03; IEC 60335-2-27,1995-05.2, “Specification for safety of household and similarelectrical appliances. Particular requirements. Skin exposureto ultraviolet and infrared radiation (International Electro-technical Commission, 1995).

13. D. Berger, “The sunburning ultraviolet meter: design and per-formance,” Photochem. Photobiol. 24, 587–593 (1976).

14. R. G. Grainger, R. E. Basher, and R. L. McKenzie, “UV-BRobertson–Berger meter characterization and field calibra-tion,” Appl. Opt. 32, 343–349 (1993).

15. http://www.solar.com/pma2101.htm.16. M. Huber, M. Blumthaler, J. Schreder, A. Bais, and C. Topalo-

glou, “Effect of ambient temperature on Robertson-Berger-type erythemal dosimeters,” Appl. Opt. 41, 4273–4277 (2002).

17. E. Muñoz, E. Monroy, F. Calle, F. Omnès, and P. Gibart,“AlGaN photodiodes for monitoring the solar UV radiation,” J.Geophys. Res. 105, 4865–4871 (2000).

18. E. Monroy, F. Calle, J. L. Pau, E. Munoz, F. Omnes, B. Beau-mont, and P. Gibart, “AlGaN-based UV photodetectors,” J.Cryst. Growth 230, 537–543 (2001).

19. A. Trevisan, S. Piovesan, A. Leonardi, M. Bertocco, P. Nicolosi,M. G. Pelizzo, and A. Angelini, “Unusual high exposure toultraviolet-C radiation,” Photochem. Photobiol. 82, 1077–1079(2006).

20. M. G. Pelizzo, P. Nicolosi, and P. Ceccherini, Italian patent,TO2005A000249, 14 April 2005; International ApplicationPCT�IB2006�000848, 11 April 2006.

21. M. G. Pelizzo, P. Ceccherini, D. Garoli, P. Masut, and P. Ni-colosi, “Absolute spectral response measurements of differentphotodiodes useful for applications in the UV spectral region,”Nonimaging Optics and Efficient Illumination Systems, R.Winston and R. J. Koshel, eds., Proc. SPIE 5529, 285–293.

22. http://metrology.hut.fi/uvnet/groups.htm.23. M. G. Pelizzo, P. Ceccherini, D. Garoli, P. Masut, and P. Ni-

colosi, “Taratura della sensibilità spettrale e caratterizzazionedi fotodiodi per le regioni spettrali dell’UVA, UVB e UVC,”presented at Metrologia & Qualità, 23–24 February 2005,Torino, Italy.


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