Diapositive 1

Choosing a solar UV simulatorChoosing a solar UV simulatorwith an appropriate spectrumwith an appropriate spectrum

François J. Christiaens and A. FourtanierFrançois J. Christiaens and A. FourtanierL´ORÉALL´ORÉAL ResearchResearch, Clichy, Clichy--FranceFrance

International Congress on PhotobiologyInternational Congress on PhotobiologySan Francisco, 1San Francisco, 1--6 July 20006 July 2000

Good afternoon,

I appreciate being able to speak to this group.

We would like to talk to you on how solar radiation and solar

simulators used in photobiological experiments compare with

another. We also want to show you a method to help choose

the best solar UV simulator.

Diapositive 2

Sunlight VariabilitySunlight Variability

Standard sunStandard sun SourcesSources Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusion

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Spec

tral

irra

dian

ce (m

W.c

m-2

.nm

-1) Zenithal sun (DIN 67501)

Morning / afternoonEarly morning / late afternoonSunrise / sunset

This slide shows a series of solar UV spectra. The most

important feature is that there is not a single ubiquitous solar

UV spectrum. Anyone outdoors will be exposed to many

different spectra, depending on sun altitude above horizon and

local weather conditions.

The sun has its zenith (i.e located just above your head) at

precise locations and given dates. The zenithal sun spectrum

(dark blue curve), defined as the “worst” case spectrum, is

given by the DIN 67501 standard.

Exposure of human skin to such a spectrum is likely to result in

intense biological effects. This spectrum will be referred as the

standard UV sun spectrum.

Diapositive 3

Ultraviolet SourcesUltraviolet Sources* Fluorescent tubes* Fluorescent tubes

Standard sunStandard sun SourcesSources Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusion

0

0.005

0.01

0.015

0.02

0.025

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance

Standard sunUVB tube1B, 6AUVA-340

We are going to show some typical UV sources which are

commonly used to simulate the solar UV spectrum in

photobiological applications.

On this slide, the spectra of fluorescent tubes are plotted.

Because sources are operated at a wide range of irradiances, a

method had to be developed for comparing each other: To

normalize the curves, measured spectral irradiances have been

divided by their total spectral irradiance. In other words, the

reciprocity law is assumed to be valid.

UVB tubes (blue curve) are typically TL12/20 when

manufactured by Philips Company or FS20 by Westinghouse.

Here, they have been filtered with Kodacel film to remove any

radiation below 290 nm. They are widely used, for example by

Dr. Kripke, Ley, Cooper etc. for phototherapy.

A combination of 1 UVB fluorescent tube with 6 UVA

fluorescent tubes (green curve) has been used and is described

in the literature (Reeve, Halliday). These tubes come from the

Westinghouse or Philips companies; in both case the spectrum

is the same.

The UVA -340 tubes come from Qpanel Co (pink curve). They

have been used by Roberts and Beasley.

Diapositive 4

Ultraviolet SourcesUltraviolet Sources* Metal halide lamps* Metal halide lamps

Standard sunStandard sun SourcesSources Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusion

0

0.005

0.01

0.015

0.02

0.025

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance

Standard sunMetal halide 1Metal halide 2

Metal halide lamps come from Dermalight or Atlas.

They emit complex spectra with intense peaks, particularly that

of mercury, and high UVA energy.

They have been used by Moyal, Lowe…, mainly for UVA

applications.

Diapositive 5

Ultraviolet SourcesUltraviolet Sources* Xenon arcs* Xenon arcs

Standard sunStandard sun SourcesSources Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusion

0

0.005

0.01

0.015

0.02

0.025

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance

Standard sunShort arc xenonLong arc xenon, WG320Long arc xenon

Short arc xenon lamps are used in Oriel and Solar Light solar

UV simulators. These sources are widely used, for example by

Dr. Kripke, Ullrich, Roberts, Sayre, Moyal, Marrot, Bernerd,

Fourtanier, Duval, Young, Guéniche…

Long arc xenon come from Atlas and are used for photostability

testing. They are also used in pharmaceutical testing.

These lamps can be filtered with a Schott WG320 to improve

the shape of the UV spectrum. This modified spectrum has

been used in photocarcinogenesis studies.

Diapositive 6

Least Square MethodLeast Square MethodComparison at each Comparison at each wavelengthwavelengthSum of the squared Sum of the squared differencesdifferences

The The lowerlower the sum, the the sum, the closer the simulator closer the simulator

spectrum to the reference spectrum to the reference spectrumspectrum

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0.005

0.01

0.015

0.02

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290 300 310 320 330 340 350 360 370 380 390 400

Wavelength (nm)

Relative

spe

ctra

l irra

dian

ce (A. U.)

Standard sun

Short arc xenon

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

After normalization of the spectra, defined with an increment

step of 1 nm, the spectrum of each candidate source is

compared to the standard sun spectrum at each wavelength.

The difference calculated at each wavelength is squared, so

that a lack at a given wavelength does not compensate for a

excess at another wavelength.

Here the spectrum of a short arc xenon lamp is being compared

to the standard sun spectrum.

Then all the squared differences are summed over the UV

waveband (290-400nm). The lower the sum, the smaller the

difference between the two spectra, the closer the simulator

spectrum to the reference spectrum.

Diapositive 7

Results: RankingResults: Ranking

-

200

400

600

800

1 000

1 200

1 400

1 600

1 800

UVB tube 1 B, 6 A UVA-340 Metalhalide 1

Metalhalide 2

Short arcxenon

Long arcxenon +WG320

Long arcxenon

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

In the table the squared spectral differences have been

reported. For example, for correctly filtered short arc xenon

lamp, the sum may be as low as 6E-4.

Then the inverse of the sum was calculated. So the higher the

inverse, the better the match. Candidate sources have been

ranked according to their inverse value.

About long arc xenon lamps: The commercially available

spectrum is plotted with a plain rectangle. The empty rectangle

stands for a long arc xenon lamp filtered with a WG320.

Correctly filtered xenon arcs sources prove to be the best match

of the standard sun spectrum.

We can also notice see that, although filtered, UVB fluorescent

tubes provide the worst solar simulation.

Diapositive 8

Considering a biological action spectrumConsidering a biological action spectrum

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

290 300 310 320 330 340 350 360 370 380 390 400

Wavelength (nm)

Rel

ativ

e ef

ficac

y (a

rbitr

ary

units

)Sp

ectr

al ir

radi

ance

(mW

.cm

-2.n

m-1

) Standard sunErythemal action spectrumStandard erythemal sun (x 100)

Now, let ’s consider that we irradiate biological systems. Most of

photobiological effects show a high dependence on the UVB

waveband. A representative, commonly used and internationally

recognized action spectrum is the erythema action spectrum,

sponsored by the Commission Internationale de l’Eclairage

(pink curve).

The “new” reference spectrum is now the efficacy spectrum of

the standard sun, i.e. the standard sun spectrum multiplied by

the erythema action spectrum (blue curve with yellow marks).

Spectra of candidate sources are multiplied by the erythema

action spectrum and they are compared to the new reference

spectrum.

Diapositive 9

Efficacy spectraEfficacy spectra* Fluorescent tubes* Fluorescent tubes

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

0.0E+0

5.0E-5

1.0E-4

1.5E-4

2.0E-4

2.5E-4

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance Standard erythemal sun

UVB tube1B, 6AUVA340 tube

Here are represented the efficacy spectra of the fluorescent

tubes. All the efficacy spectra show a strong peak in the UVB

waveband.

The efficacy spectrum of UVB fluorescent tubes do not follow

the standard sun efficacy spectrum.

When 6 UVA fluorescent tubes are combined with one UVB

tube, the resulting efficacy spectrum is almost superimposed to

the UVB alone efficacy spectrum.

The UVA-340 tube efficacy spectrum shows the best match, in

the fluorescent tubes family.

Diapositive 10

Efficacy spectraEfficacy spectra* Metal halide lamps* Metal halide lamps

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

0.0E+0

5.0E-5

1.0E-4

1.5E-4

2.0E-4

2.5E-4

3.0E-4

3.5E-4

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance Standard erythemal sun

Metal halide 1Metal halide 2

On this slide, efficacy spectra of metal halide lamps show big

discrepancies with the standard sun efficacy spectrum, in the

UV range.

Diapositive 11

Efficacy spectraEfficacy spectra* Xenon arcs* Xenon arcs

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

0.0E+0

5.0E-5

1.0E-4

1.5E-4

2.0E-4

2.5E-4

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

ativ

e sp

ectr

al ir

radi

ance Standard erythemal sun

Short arc xenon

Long arc xenon, WG320

Long arc xenon

Last but not least, xenon arcs efficacy spectra are very close to

the standard sun efficacy spectrum. Commercially available

long arc xenon, plotted in violet, may be re-filtered so that its

efficacy spectrum becomes much closer to the reference

spectrum.

Diapositive 12

Results: Ranking of efficacy spectraResults: Ranking of efficacy spectra

0.0E+00

2.0E+07

4.0E+07

6.0E+07

8.0E+07

1.0E+08

1.2E+08

1.4E+08

1.6E+08

UVB tube 1B, 6A UVA340tube

Metalhalide 1

Metalhalide 2

Short arcxenon

Long arcxenon +WG320

Long arcxenon

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

The least square method, described above, is applied again.

Again, correctly filtered the xenon arc sources provide the best

solar UV simulators, by far.

Ranking is different for UVA-340 fluorescent tube and for long-

arc xenon lamps. However, correctly filtered xenon lamps still

provide the best matching spectra.

Diapositive 13

SummarySummary

Xenon based solar UV simulators have a spectrum close to theXenon based solar UV simulators have a spectrum close to thestandard UV sunstandard UV sun

This ranking is valid whether the action spectrum is known or noThis ranking is valid whether the action spectrum is known or nott

Special attention must be paid to the short wavelength filtratioSpecial attention must be paid to the short wavelength filtration n

Standard sunStandard sun Physical spectra matchPhysical spectra match Biological spectra matchBiological spectra match ConclusionConclusionSourcesSources

These are the thoughts that I wish to leave you with.

Often, the spectrum of a UV source is said to be close to the

sun peremptorily. We have presented a method to rank the

different laboratory sources according to the closeness of their

spectrum to the solar spectrum. The results show that xenon

based solar UV simulators reproduce the solar UV spectrum

very closely.

Thus, from the physical point of view as well from the erythemal

point of view, xenon based solar UV simulators are the best

choice.

Furthermore, it is clearly possibly to filter solar simulators to

closely match sunlight and its erythemal risk.

A WG-320 of convenient thickness removes irrelevant UVB and

UVC rays.

Thank you for your attention.

Diapositive 14

Consequences for SPF when solar simulator spectra Consequences for SPF when solar simulator spectra deviate from the spectrum of the sundeviate from the spectrum of the sunSPF 15 sunscreen absorption

1

6

11

16

21

26

31

36

290 300 310 320 330 340 350 360 370 380 390 400

Wavelength (nm)

Mon

ochr

omat

ic P

rote

ctio

n Fa

ctor

1

6

11

16

21

26

31

36

UVBtube

1 B et 6A

UVA-340 Metalhalide 1(Atlas)

Metalhalide 2(Hönle)

Shortarc

xenon

Longarc

xenon +WG320

Longarc

xenon

SPF

This slide shows a direct result on what happens on Sun

Protection Factor when it is assessed using sources whose

spectra deviate from the spectrum of the sun.

Here (upper chart) we assume that the sunscreen absorbs

mainly in the UVB waveband, to provide some protection

against erythema. It is not indirectly linked to existing absorbers.

The lower chart shows the gaps between SPFs that would be

measured with different solar UV simulators. The SPF baseline

is set at 15. We can notice that SPF is strongly overestimated

when assessed with fluorescent tubes.

These results are in full agreement with those found in vivo by

Uhlmann et al. in 1996 (Int.J.Cosm.Sci. 18, 13-24) and by Noda,

Kawada et al. in 1992 (J.Dermatol. 19, 465-469).