159
Ultraviolet Radiation
Ultraviolet Radiation
What is it?
• Photons
• Energies between X-rays and visible light
• Natural and man-made exposure
Why Do We Care?
• Skin cancer
• Other effects in the skin
• Immunosuppression
• Eye damage
Why Do We Care?
• Regulatory
– Not much
– Radiation Emitting Devices Act (REDA or RED Act) for tanning beds
Physical Principles
Biological Divisions
UV-C UV-B UV-A Ionizing Visible
Energy (eV)
Wavelength (nm)
12.4 4.4 3.9 3.1
100 280 320 400
1240E
UV-C
• Ionization energy for water 12.4 eV
• UV-C 100 ≤ ≤ 280 nm
• “Germicidal”
• Exposure only from manufactured sources
UV-B
• 280 ≤ ≤ 320 nm
– Was 315 nm based on erythema action spectrum; current wavelength based on DNA damage
• Erythema-inducing region
• “Direct action” damage
• Hazardous solar ultraviolet
UV-A
• 320 ≤ ≤ 400 nm
• “Blacklight”
• “Indirect action” damage
• Induces fluorescence in many substances
Physical Divisions
Vacuum Far UV Near UV Ionizing Visible
Wavelength (nm)
100 190 300 400
Sources
Man-Made Sources
Man-Made Sources
• Incandescent
• Gas discharges
• Electrical discharges
• Fluorescent lamps
• Lasers
Incandescent
• “Blackbody” sources
• Very inefficient (0.1 – 0.2%)
• Rarely used for UV production
– Previously used for small spaces, e.g. dashboard phosphors
Gas Discharge
~
Gas Discharge
• Electrodes: W, Mo, Ta typical
• Glass walls
– Fused silica (quartz) 190nm
– “Suprasil” quartz 165nm
– Ti alloy doping to filter UV-C
– Filtering to block visible light
• Gases: Hg typical (10 – 25% UV)
– Inert; metal halides in high pressure lamps to increase output
Low Pressure Lamps
• 1 Pa, 500 K
• Discrete lines
High Pressure Lamps
• 1 MPa, 6000 – 8000K
Electrical Discharges
• “Arcs” in free air
• Spectrum depends on electrode composition
– W – arc welding; C – electrodes consumed
• Occupational hazard for arc welders
Fluorescent Lamps
• Low pressure Hg lamp (253.7nm main emission) with phosphor coating to convert UV into visible or UVA
• Blacklight phosphor (350 – 400nm) to induce fluorescence
• Sunlamp emission 280 – 400nm
UV Lasers
• Gas: He-Cd (325nm), N (337nm), excimer (various)
• Solid state: Nd:YAG frequency quadrupled (1064 → 266nm) using non-linear optical components
Solar UV
Solar UV
• Emitted from surface of sun
• Blackbody-like radiation 5600K
Solar UV at Sea Level
Wavelength
band
UV-C UV-B UV-A VIS NIR
Irradiance
(W/m2)
0 1 50 500 450
Terrestrial UV typically limited to > 290 nm due
to attenuation by ozone.
Variations in Intensity
Pathlength
• Latitude
• Season
• Altitude
Attenuators
• Ozone concentration
• Aerosols
• Smoke/Dust
• Rain
Attenuation of UV
Attenuation
• Absorption (ozone, oxygen, aerosolized water)
• Scattering (smoke, dust, other aerosols)
– Rayleigh
– Mie (“large” mm particles)
Aside: Rayleigh Scattering
• Elastic scattering of EM waves by particles much smaller than the wavelength
Aside: Mie Scattering
• Particle size comparable to or larger than wavelength
• Solution to Maxwell’s equations
Geometry
a
dO
d
Ozone: mO
Atmosphere
mR, mM
Direct Solar UV Irradiance
• a: solar zenith angle
• d: atmosphere thickness
• dO: ozone thickness (~0.32cm at STP)
• mR,M,O: Rayleigh, Mie scatter coefficients, ozone absorption coefficient
ammma seccos OOMR dd
o eEE
Aside: Irradiance
• What is it??
• Defined as the “radiant power incident on an infinitesimal surface element containing the point of interest, divided by the area of that surface element”.
– “Power density”, “Flux density” …
• Not to be confused with fluence rate, which is used for free space rather than a surface.
Geometry
a
dO
d
Ozone: mO
Atmosphere
mR, mM
Estimating Solar Altitude for Time of Day
80equinox for vernal
1day 1 Jan year ofday
plane eliptical tilt wrt sEarth'4.23
3652sinsinsin
plane equatorial & line
Earth-to-sun between angle ndeclinatiosolar
noonsolar after hr per 15 anglehour solar
latitude geographic
sinsincoscoscossin
o
max
max
1
o
dd
d
dd
h
ve
ve
How Do We Use These Equations?
• Many calculations involve numerical integration or heavy approximation
– Changes in UV attenuation in the atmosphere
– Estimating dose (e.g. changing the time of day you walk)
– Changes in cancer incidence due to either of the above
Attenuation Changes
• Ozone column/thickness of atmosphere, attenuation coefficient, time of day/year changes
– Calculations often relative to something else
– Ozone attenuation usually dominates scattering
ammma seccos OOMR dd
o eEE
Estimating UV Dose
• Integral of E() over wavelength (), time of day (t), days of the year (day)
• Use relationship h=90-a to bring time variables into play
– May be easier to substitute dt for d (see Solar Altitude calculation)
a am
dddaydteSE ood
o cossec
Solar UV “Dose”
• Standard Erythema Dose (SED) = 100 J/m2
erythemally weighted
• Minimum Erythema Dose (MED) is the weighted UV dose required to initiate erythema in an individual (clinical measure), about 200 J/m2 erythemally weighted
Intensity: Solar Altitude
Solar altitude h = 90 - a
Solar altitude h = 90 - a
Intensity: Ozone
Intensity: Altitude
• dE/E ~ +4% (net) for each 300 m above sea level
– Direct UV irradiance increases
– Scattered UV decreases
Intensity: Latitude
Intensity: Cloud Cover
Intensity: Seasonal Variations
Intensity: Surface Reflections
Practical Points
• Water is a weak reflector (<5%) and a poor absorber (>40% transmission through 50cm) of UV-B
– Sunburn under water
Practical Points
• Solar irradiance at sea level ~50% scattered and ~50% direct
– Exposure under localized clouds or in the shade
Practical Points
• Window glass absorbs UV-B strongly
– Longer to sunburn behind glass
Practical Points
• Sunlamps with UV-B filters not necessarily “safe”
• UV-A still causes
– Aging (“dermatoheliosis”)
– Immunosupression
– Erythema (much less than UV-B)
Interactions with Tissues
What Tissues?
• Skin
• Eyes
• Oral cavity (dentistry)
What Interactions?
• Absorption, primarily
– Scattering negligible (short pathlength)
• Important biomolecules
– Nucleic acids (pyrimidines: cytosine, thymine)
– Amino acids in proteins (tyrosine, tryptophan)
• Chromophores (melanin, hemoglobin, carotenes)
Nucleic Acids
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
220 245 270 295 320
Cytosine
Thymine
Exti
nct
ion
Co
effi
cie
nt
(cm
-1 M
-1)
Wavelength (nm)
Amino Acids
Amino Acids
0
2000
4000
6000
8000
10000
12000
14000
220 270 320
Phenylalanine
Tryptophan
Tyrosine
Exti
nct
ion
Co
effi
cie
nt
(cm
-1 M
-1)
Wavelength (nm)
Chromophores
0
100000
200000
300000
400000
500000
600000
700000
800000
200 300 400 500 600 700 800
Melanin
HbO2
Hb
beta-Carotene
x 100
Exti
nct
ion
Co
effi
cie
nt
(cm
-1 M
-1)
Wavelength (nm)
Attenuation in the Skin
~200 µm
~1-4 mm
Attenuation in the Skin
Practically all UV absorbed in the epidermis
Attenuation in the Eye
Attenuation in the Eye
UV Photochemistry
• UV absorption by molecules generates photoproducts
• Principal target for UV is DNA
• Photoproducts constitute:
– Pyrimidine dimers (UV-B direct action)
– Single strand breaks (UV-A indirect action from OH●)
UV Photochemistry
1. Absorption 2. Fluorescence 3. Phosphorescence 4. Vibrational relaxation 5. Internal Conversion 6. Intersystem Crossing 7. Quenching
Energ
y
Ground electronic state (singlet)
First excited singlet state
First excited triplet state
1 3
2
5
4
6
7 4
4
4
7
UV Photochemistry
• Excited singlet or triplet state may:
– React with another molecule
– Transfer its energy / electron spin to another molecule
– Break apart (common source of OH●)
UV Photosensitivity
• UV interacts with exogenous molecules (photosensitizers) to produce a biologically strong reactant
• “Photodermatosis”: rashes, et cetera that appear after exposure to sun
UV Photosensitivity
• Light sensitivity diseases
– Polymorphic light eruption (looks like boils)
– Actinic reticuloid (chronic inflammation upon sun exposure)
– Solar urticaria (hives)
– Porphyria (over production and accumulation of porphyrins)
UV Photosensitizers
• Things you might not expect...
– Phenobarbitone (hypnotics)
– Chlorpromazine (tranquilizer)
– Thiazide (diuretics)
– Tetracyclines & sulphurs (antibiotics)
– Cosmetics containing eosin or psoralens
UV Photosensitizers
• Intentional (clinical) use
– Methoxypsoralens (e.g. 8-MOP) causes cross-linking to prevent DNA replication
– Hematoporphyrin derivative (HPD) for photodynamic therapy (skin sensitivity a few weeks after treatment)
UV Photosensitization
OXXO
OSOT
*
2
1
*
2
1
2
3*
Quenching Singlet Oxygen
• Quenchers de-excite the singlet oxygen prior to it reacting with anything useful
– Collisional quenching (energy transfer)
– Static quenching (binding)
• Common quenchers
– Vitamin E
– Carotenes
– Ascorbic acid (vitamin C)
Biological Effects
Cellular Level Effects
• Melanogenesis
– DNA damage
– Activation of tyrosinase
– Liberation of cell membrane lipids
• Immunosuppression
– Decrease in Langerhans cells (T-cell antigens)
– Change urocanic acid trans to cis
– Alter epidermal cytokine production
Cellular Level Effects
• Carcinogenesis
– Activation of oncogenes
– Inactivation of tumour suppressor genes
• Cell growth arrest
• Apoptosis
– Both mainly during UV sterilization
Organ Level Effects
• Stochastic
– Probability increases with dose
• Deterministic
– Severity increases with dose beyond some threshold
• Effects are somatic
– No inheritable genetic damage
Responses To UV
Skin
Attenuation in the Skin
~200 µm
~1-4 mm
Attenuation in the Skin
Practically all UV absorbed in the epidermis
Deterministic Effects
• Erythema & subsequent melanogenesis
– Inflammatory response – epidermal & dermal vasodilation
– Mechanisms – direct action on vessels, indirect action in response to diffusion of prostaglandins in the epidermis to the dermis, response to DNA damage
– Edema, pain, blistering at high UV doses
– Thickening of the stratum corneum (3-5x)
Blood Flow in the Skin
Erythema Time Course
Early onset
erythema
High UV dose
Late onset
erythema visible
MED exposures
Maximum
erythema
Erythema
fades
Immediate pigment
darkening (IPD)
Delayed melanogenesis
becomes noticeable
0 4 1-2 12-24 hours 1-2 days
Minimal Erythemal Dose
• MED
• Minimum biologically effective dose (really radiant exposure) required to induce erythema in an individual (~ 200 J/m2 in melano-compromised individuals)
• Highly dependent on individual factors, standard erythema dose ( 1 SED = 100 J/m2) introduced for standardization
Skin Types
Fitzpatrick et al. 1975
Skin Types
1 SED = 100 J/m²
Biologically Effective Irradiance
• E(): Spectral Irradiance (W/m²/nm)
• S(): Biological Effectiveness curve
– e.g. erythema action spectrum
dSEEeff
Erythema Action Spectrum
Erythema Action Spectrum
CIE (1998) ▬
Anders (1995) ▲
CIE (1935) ■
CIE: International Commission on Illumination
Wavelength Dependence of MED
Erythema Action Spectrum, In Action
• Small changes in UV-B (different ozone conditions) can result in large changes to biologically effective dose (FxB)
Aside: Dobson Units
• 1 DU = 10 µm of ozone at STP
• Reference level is 220 DU, corresponding to development of the Antarctica ozone hole
Aside: SPF
• Sun Protection Factor
• Really a dose reduction factor
– e.g. SPF 15 reduces dose to skin by 15x
– Dactual = Do/SPF
Melanin Production
• “Melanogenesis”
• Produced in melanocytes in basal layer
– Boundary between epidermis & dermis
• Melanin redistributes to keratinocytes in epidermis
• Skin pigmentation (“tanning”) and thickening (“conditioning”) may increase MED for UV-B exposure at least 4x
Deterministic Effects
• Immunosuppression
– Loss of epidermal antigen presenting Langerhans cells
– Alteration of urocanic acid (trans to cis) activates “suppressor T-cells”
Deterministic Effects
• Aging of the skin – “Late effect”
– Structural changes in the dermis
– Dryness, loss of elasticity, mottled complexion, deep wrinkling
– Difficult to determine action spectrum due to long term nature of the changes
• Actinic Keratosis (AK) – hard, precancerous skin lesions
Deterministic Effects
• Vitamin D production
– Conversion of 7-dehydrocholesterol in epidermis to D3 previtamin
– Conversion in liver to useful 25-hydroxyvitamin D
– D3 broken down by UV
– Only 15 minutes exposure to hands, arms, face, during spring to fall on a clear day
Stochastic Effects
• Cancer
– Basal cell, squamous cell: highly treatable
– Malignant melanoma: challenging
• Modeling skin cancer incidence
– Rate of Incidence, UV Dose, amPlification factor
pDI
BCC/SCC
• Both highly treatable (99% CR BCC, 97% CR SCC)
• Mainly UV-B
• p~2.5 SCC, ~1.5 BCC
• Higher incidence with lower pigmentation
• Incidence ~50% in Americans age>65
• Unknown latency
• SCC often accompanied by AK
Non-Melanoma Action Spectrum
Relative Risk for BCC/SCC
Melanoma
• Highly metastatic
• Action spectrum is unknown, although UV-B irradiation seems to be the main risk
• Often found on covered regions (e.g. trunk) – “Acute exposure hypothesis”
• 10-15 year latency
• Rising incidence (doubles every ~15 yrs)
The Eye
Attenuation in the Eye
Attenuation in the Eye
Exposure Levels Required To Produce Ocular Effects
Mainly in the cornea and conjunctiva.
Deterministic Effects
• Conjunctivitis (conjunctiva)
• Photokeratitis (cornea)
– Welder’s flash, arc eye, snow blindness
– Primarily caused by excessive UV-B
– Inflammation of the cornea, resolves spontaneously in about 36 hours
– Thresholds 270nm (~50), 310nm (~550), 315nm (~22,500 J/m²)
Deterministic Effects
• Cataract formation
– Evidence from animal models and human epidemiology, 295 – 320 nm range
– Relatively high exposures required (> 5 MED for transient cataracts)
• Retinal damage
– Not observed (< 1% UV-A penetration)
Stochastic Effects
• Tumours
– Some epidemiological evidence of ocular melanoma
– Choroid & ciliary body melanomas positively correlated with time outdoors (Australian study: Vajdic 2002)
– Hypothesis that UV exposure from the horizon rather than overhead
Medical Applications
Phototherapy
• UV-B for skin conditions such as:
– Psoriasis (scaling due to rapid cell division)
– Vitiligo (depigmentation, possibly due to autoimmune effects)
– Atopic dermatitis / eczema (chronic rash, may be heriditary)
• Light source tends to be fluorescent lightbulbs with various filter materials added to select spectral content
Phototherapy
• Psoriasis
– Suppresses cell division, changes the inflammatory environment of the site
Phototherapy
• Vitiligo
– Suppresses immune system in irradiated region
Phototherapy
• Eczema
– Helps to suppress inflammatory response
Phototherapy
• Old school – broad band ultraviolet A+B
Images from Solarc Systems
Phototherapy
• New school – narrow band UV-B (311 nm)
– Minimizes erythema while catching the edge of the psoriasis/vitiligo “action spectrum”
Images from Solarc Systems
PUVA Therapy
• Psoralen + UV-A
– Psoriasis (scaling of the skin) & vitiligo (autoimmune/inflammatory depigmentation)
– Cutaneous T-cell lymphoma (photophoresis technique)
– 8-MOP (methoxy psoralen, topic or oral) + UV-A (360nm)
Psoralens
• 3 ring compounds that bind to DNA non-covalently
• Irradiation @ 365nm causes covalent binding to thiamine, and subsequent irreversible cross-linking
• Fatal to healthy cells
General psoralen structure
8-methoxy psoralen
Extra-Corporal Photopheresis
Damaged white blood cells
recognized by immune system,
which makes healthy lymphocytes
to fight against those abnormal cells.
Treatment is used for cutaneous
T-cell lymphoma.
Neonatal Jaundice
• “Hyperbilirubinemia”
• 10 – 20% of newborns
• Excessive bilirubin photodecomposed by UV-A and blue light (400 – 480nm)
Dentistry
• Polymerization of resins
• Fluorescence of tooth enamel
– Decreased fluorescence in the vicinity of cavities
– Not used routinely
Pathology/Biology/Other
• Sterilization of air and flow hoods in various biological laboratories
• New UV-C based technologies used for terminal cleaning of hospital rooms
– High intensity pulsed xenon arc lamps
– 1 pulse is enough to exceed the occupational effective limit of 30 J/m² (coming up)
Detection & Dosimetry
Terms & Units
Symbol Name Relationship Units
Q Radiant energy J
φ Radiant flux ∂Q/∂t W
I Radiant
intensity ∂φ/∂Ω W/sr
L Radiance ∂φ/∂Ω/∂s W/m²/sr
E Irradiance ∂φ/∂s W/m²
H Radiant
exposure ∂Q/∂s J/m²
Biologically Effective Irradiance
• Recall:
dSEEeff
Detection Theory
• Rather than biologically effective irradiance we measure:
• In practice, a correction factor is applied so signal can be directly correlated to a dosimetric quantity (e.g. SED/MED)
dGESignal
dGE
dSECF
known
known
UV Dosimeters
• Thermal
• Photon counting
• Chemical
• “Biological”
Thermopile Detectors
• Incorporated into “Pyranometers”
• Principle: Voltage α ∆T
• Sensitivity: 10 µV / [W/m²]
• Accuracy: ±1% typical
• Spectrum: 250 – 2000 nm
• Uses: Secondary calibration standards, field instruments
Thermopile Detectors
V
Envelope
Thin
window
Pt electrode Heat sink
Receiver
(Au, Pt)
Semiconductor
Photon Counting
• Photomultiplier tube
• Photodiode
Photomultiplier Tubes
• Principle: photoelectrons from photocathode multiplied by accelerating through a series of dynodes
• Advantages: very high sensitivity
• Problems: fragile, stable voltage required
• Uses: measuring low irradiances
Photomultiplier Tubes
Photodiodes
• Principle: photoconductivity (reverse bias) or photovoltaic (no applied voltage – photoelectric current only)
• Advantages: inexpensive, stable, robust
• Disadvantages: poor UV sensitivity
• Uses: routine portable usage
Photodiodes
Chemical Sensors
• “Actinometry”
• Principle: absorbed photon induces a detectable chemical change
• Advantages: passive device (no p/s required)
• Disadvantages: calibration, reproducibility
• Uses: dosimetry in microbiological specimens
Biological Sensors
• Real systems
– Example: determine a treatment time based on erythema onset on a small patch of skin
• Simulated
– Attempt to match the “detector’s” response G() to some appropriate action spectrum S()
– Problems: person-to-person S() variability, small mismatches may amplify dose differences, angular response of detector same as what is being modeled?
Protective Measures
General Health & Safety
• Administrative Controls
• Engineering Controls
• Personal Controls
Administrative Controls
• Limit access (necessary personnel only)
• Information on hazards (education, policies and procedures)
• Signs and warning lights
• Substitution
• Distance and time limits (based on MPE)
Engineering Controls
• Containment (barriers, instrument housing)
• Machine guards
• Interlocking (device turns off or doesn’t operate under certain conditions)
• Screens, UV filters
• Elimination of reflective surfaces
Personal Controls
• Personal Protective Equipment (PPE)
• Skin
– Clothing is best
– UV-A+B sunblocks, but industrial setting UV-C may also be a concern (SPF 30 minimum preferred)
• Eyes
– Glasses: opaque for <400nm, side shields, good visible transmission
– Welding shades: helmet or mask with filters
Ozone Production
• UV-C produces ozone in air <260nm
• Smell sensitivity ~ 0.1 ppm
• Occupational limits in Ontario
– 0.1 ppm daily average, 0.3 ppm 15 minute exposure
• Lethal concentration ~ 50 ppm for 0.5 hours
Exposure Standards
Historical
• CIE (1935) – Standard erythema curve
• AMA (1942) – 1 EU = 100 mW/cm2 * S(297)/S()
• NRPB, NIOSH (1977, 1972) – Modern standards
– 2004 International Commission on Non-Ionizing Radiation Protection (ICNIRP)
Radiation Protection from Modern Standards
• Based on an envelope action spectrum incorporating erythema and photokeratitis
• Not valid for photosensitive individuals (type 1 skin)
• Sets effective exposure limits
• NO CANADIAN STANDARDS (or US, really)
– American Conference of Governmental Industrial Hygienists (ACGIH)
• 30 J/m² “Threshold Limit Value”
Ontario Ministry Of Labour
• “…an employer shall take every precaution reasonable…” (s.25(2)(h) of the Occupational Health & Safety Act)
• MoL uses ACGIH exposure guidelines to establish if a workplace is using due diligence in protecting its workers
• Guidelines do not apply to workers using UV lasers or hypersensitizing substances
Envelope Action Spectrum
ICNIRP 2004
Envelope Action Spectrum
Effective Irradiance and Exposure
dttEH
dSH
dttEH
dStEtE
T
T
effeff
eff
0
0
,
,
Polychromatic & UV-B Exposure
• UV-B exposure limit chosen conservatively
– 30 J/m² of Effective Radiant Exposure
– Total over any 8 hour period
• Tabulated as Radiant Exposure limits for monochromatic radiation
• Compare with MED
ICNIRP 2004
MPE Based on Effective Irradiance
30 J/m2 maximum exposure (UV-B&C) ICNIRP 2004 (ACGIH uses same table) NIOSH uses 254nm as reference, so permits 0.2 µW/cm² for 8 hours or 100 µW/cm² for 1 minute (2x above, why?)
Maximum Permissible Exposure (8h Period)
UV-A Exposure
• Maximum permissible exposure (MPE) based on irradiance (long times) or radiant exposure (short times)
• 10 W/m² for t > 10³ s
• 10 kJ/m² for t < 10³ s
– Why?
• No annual exposure limit
Associated Regulators / Regulations
• Radiation Emitting Devices Act & Regulations (Tanning Equipment)
– Canadian regulations administered by Health Canada
• ICNIRP & WHO reports
• EC Health & Consumer Protection Directorate-General
• Ministry of Labour (Ontario)
REDA
• “Radiation” means energy in the form of electromagnetic waves or acoustical waves
• “Radiation emitting device” means
– (a) any device that is capable of producing and emitting radiation, and
– (b) any component of or accessory to a device described in paragraph (a)
REDA
• Prohibits the sale, lease, or importation of any radiation emitting device in Canada that:
• (a) does not comply with the standards, if any, prescribed under paragraph 13(1)(b) and applicable thereto; or
• (b) creates a risk to any person of genetic or personal injury, impairment of health or death from radiation by reason of the fact that it – (i) does not perform according to the performance
characteristics claimed for it, – (ii) does not accomplish its claimed purpose, or – (iii) emits radiation that is not necessary in order for it to
accomplish its claimed purpose.
REDA
13.1(b) The Governor in Council may make regulations prescribing standards regulating the design, construction and functioning of any prescribed class of radiation emitting devices for the purpose of protecting persons against genetic or personal injury, impairment of health or death from radiation.
REDA
• Governor in Council = Prime Minister + Cabinet – Executive authority is vested in the Crown
• Acts versus Regulations – Laws passed by a legislative body versus directions
adopted by the executive branch that have the binding effect of law. Generalized laws are often passed that empower a particular department of the executive branch (through the appropriate cabinet minister) to make regulations to implement the intent of the general law.
REDA
• Prohibits deceptive claims
• Sets regulations for labeling, packaging, safety and functional features, and advertising
Tanning Equipment Regulations In Canada
• “Tanning equipment” means a device that – Can be equipped with one or more ultraviolet lamps
– Induces skin tanning or other cosmetic effects and is advertised as inducing such effects.
• No occupational UV standards, but… – “Prevent over exposure” – any dose that exceeds the
amount required to produce daily vitamin D requirement
– “Tanning is not safe”, but the evidence is not strong enough to ban tanning equipment (regulations FAQ)
Tanning Equipment Regulations In Canada
• Exposure time calculations – 100 J/m2 for the first session, and up to 625 J/m2
per session beyond the first (usually increase gradually)
– Similar to FDA dosing schedule, but uses CIE(1998) action spectrum from previous lectures (unlike FDA)
ES
mJDose
Time2
