The optical radiation is defined as any electromagnetic radiation in the wavelength range between 100 nm and 1 mm. The spectrum of optical radiation is divided into ultraviolet radiation, visible radiation and infrared radiation For the purposes of protection, optical radiations are further subdivided in:
Ultraviolet radiation: optical radiation of wavelength range between 100 nm and 400 nm. The ultraviolet region is divided into UVA (315-400 nm), UVB (280-315 nm) and UVC (100-280 nm);
Visible radiation: optical radiation of wavelength range between 380 nm and 780 nm;
Infrared radiation: optical radiation of wavelength range between 780 nm and 1 mm. The infrared region is divided into IRA (780-1400 nm), IRB (1400-3000 nm) and IRC (3000 nm-1 mm).
The optical radiation sources can be classified as coherent and non-coherent sources.
The formers emit in phase radiations (minimums and maximums overlap) and are generated by LASERS, whereas the latters emit out of phase radiations and are generated by all the other non LASER sources and by the sun.
Main adverse effects caused by optical radiation on the eye and the skin
The typology of the effects associated with exposure to AOR depends on the wavelength of the incident radiation, whereas the intensity determines both the possibility that these effects occur and their gravity.
The interaction of optical radiation with the eye and the skin can have harmful consequences as reported in the following table:
100 - 280
Accelerated process of skin ageing
280 - 315
315 - 400
400 – 780
Photochemical and thermal injury to the retina
780 - 1400
1400 - 3000
3000 - 106
Besides the risks to the health arising from direct exposure to artificial optical radiation, further risks must be taken into account:
overexposure to visible light: temporary disorders of vision, such as dazzling, temporary blindness;
risks of fire and explosion triggered by the source itself and/or by the radiation beam;
and further risks associated with appliances/work practices that use AOR such as thermal stress, contact with hot surfaces, electrical, explosion or fire risks such as in the case of use of high power LASERs etc.
The kind of the effects, their gravity or the probability to occur, depend on the radiant exposure, the wavelength and, concerning some effects on the skin, on the individual photosensitivity, which is a genetically determined feature.
The effects produced on the eye and the skin can be classified depending on their temporal course into:
rapidly occurring or acute exposure effects, with a lag period of hours or days;
long term or chronic exposure effects, with a lag period of months or years.
Generally, it is possible to establish, for each acute effect, “the threshold dose” below which the effect does not occur. Most of the long term effects (tumours: skin cancer) are fundamentally different from the acute effects and their probability to occur depends on the dose accumulated by the individual.
Effects on the eye
For the purposes of vision, the eye must be necessarily exposed to the light.
Nearly all visible light sources (the sun and the lighting lamps) emit also non visible radiations such as: infrared radiation and, to a lesser extent, ultraviolet radiation, that are useless for vision but that, on the other hand, can represent a potential risk to the eye.
With respect to the radiation propagation through the ocular structure, the eye can be schematized as a system of superposed filters, each of them having a particular spectral transmission (passing band) and thus capable of absorbing and "filtering" specific wavelengths.
The biological effects produced by UVR on each structure, depend on:
a) the absorbed dose that, on its turn, is related also to the filtering properties of the preceding structures, that can completely absorb the radiation of specific wavelengths;
b) the intrinsic absorption features of the structure taken into account;
c) the susceptibility of the concerned tissues to absorb UVR;
d) the capacity of repairing the damage produced.
The spectral transmission of the lens varies progressively with the age and this can influence both the kind of risk and the level of risk. Lens removal and its substitution with an artificial prosthesis, when surgically treating the cataracts, can considerably affect the eye transmission in the UV-A spectral region and increase retinal exposure.
The most significant adverse effects that can be seen on the non protected eye structures when they are exposed to UVR and the spectral regions in which they can be seen are:
1) the photokeratoconjunctivitis (180÷330 nm);
2) the lens damages that can accelerate the cataract onset (290÷340 nm);
3) the retinal damage of photochemical type in the aphakic individual (300÷550nm).
It is due to short and intense exposures to UVR of the spectral region indicated above. It is an effect characterised by superficial lesions of the conjunctiva and the cornea, due to the death and the progressive loss of epithelial cells that results in uncovering superficial nerve terminations, that come into contact with the lachrymal film. The resulting inflammatory condition is temporary and reversible, but it is associated with acute pain, photophobia and an irritating "feeling of sand" in the eyes. The action spectrum of photokeratitis present a maximum of biological efficacy between 265 and 275 nm. The prevention can be easily achieved by the means of suitable goggles or masks equipped with a filter.
Functionally, the cristalline lens is a variable focal lens and, by definition, must be clear in the visible band. The term cataract defines a pathological status characterised by a more or less marked opacity of the lens, corresponding to a reduced light transmission to the retina and to an increase of the diffuse component.
The cataract is mainly a multifactorial pathology of the older age, due to molecular and cellular ageing processes.
However, the UV radiation is capable to accelerate all these processes and thus it must be considered as a specific causal risk. Several epidemiological investigations have demonstrated this association, and also the experiments performed on different animals highlight the cataractogenic effect of UVR.
The contribution to the cataract induction of UVR exposure is an effect having a remarkable health care effect both for the severity of the pathology and for its social costs. The microscopical lesions that contribute to accelerate the cataract onset are of the photochemical type. They basically depend on the UVR dose absorbed by the lens and, due to the extreme slowness of the repairing processes, they accumulate over the time.
Concerning infrared radiation exposure that is emitted, for example, by incandescent bodies, such as melted glass or metal, since the beginning of XX century, several reviews and epidemiological studies have highlighted a significant increase in the incidence of cataract among workers in charge of glass and metal working activities at melting temperatures.
For ocular exposure to visible or to infrared-A (I.R. - A) light, the cataract is associated to absorption of radiation into the iris: the thermal energy is then transferred by direct conduction to the lens epithelial tissue.
For ocular exposure to infrared radiation with dominant spectral components in the IR-B and IR-C regions, the radiation is, on the other hand, absorbed by the cornea: the thermal energy spreads then to the lens by thermal conduction through the adjacent ocular tissues (cornea-aqueous humour).
The visible radiation and the I.R. radiation are both capable of inducing cataract, by producing, in both cases, even if by different mechanisms, the heating of the lens. For the glass-maker's cataract, this should be associated basically to IR-B and IR-C exposure.
Based on the localisation of the opacity, three main cataract forms can be defined:
1) the nuclear cataract, characterized by a progressive yellowing of the nuclear proteins and by the formation of macromolecular aggregates that increase light diffusion;
2) the posterior subcapsular cataract, in which the opacity is due to an aggregation of degenerated and abnormal cells on the posterior surface of the lens;
3) the cortical cataract, characterized by small vacuoles that fill up with water and cortical fragments.
The retinal injury from blue light
In a normal adult individual the retina is not reached by UVR, excepted for a very little UV-A fraction of lower energy. The global filter function (bandpassing, because it transmits by skipping the visible and the infrared A) is carried out by the ocular structures preceding the retina. However, in the juvenile age the eye presents a higher transparency to the UVR and alsa in the aphakic individuals (natural lens replaced by a prosthesis) the transmission in the UV-A region can be considerably increased.
Until few years ago, it was thought that the damages produced by optical radiation on the retina were basically of thermal nature. It has then been demonstrated that the radiation in the spectral region between 300 and 550 nm can induce photochemical damages on the retina. According to some experts, these damages could concur to accelerate the appearance of age related macular degeneration.
Effects on the skin
The most relevant effects that can occur on the skin following an acute and/or chronic exposure to UVR are:
a) the photoelastosis, that is associated with the photoageing of the skin (220÷440 nm);
b) the photocarcinogenesis of the skin (270÷400 nm);
c) the erythema (200÷400 nm);
d) the phototoxic and photoallergic reactions (280÷400 nm);
e) the UVR immunosuppression (250÷400 nm);
f) the true adaptive pigmentation (tanning) (200÷400 nm).
The erythema due to UVR exposure is the most studied and probably most known biological response of the skin. The effect can be easily observed, especially in the fair skin individuals. The erythemagenic reaction is highlighted by a reddening of the skin, that indicates a peripheral vasodilatation, that reaches the maximum after 12-14 hours and clears up in 3-4 days.
In the field of protection against the harmful UVR effects on the skin, the erythema has a remarkable relevance because:
1) among all the effects induced by UVR, the erythema is the one that probably corresponds more than any other to the definition of deterministic effect;
2) the erythemagenic response, both in terms of action spectrum and of dose-response, is the most representative phenomenon of the individual skin photosensitivity.
Photoageing of the skin
The ageing of the skin is a complex and multifactorial phenomenon and is the result of the chronological ageing and of the photoageing due to the overall UVR exposure. The photoageing occurs in a more or less marked way in the worst photoexposed areas, such as arms, face and neck, and is characterized by skin dryness, generally thickened epidermis, wrinkledness, loss of elasticity, irregular pigmentation.
It is thought that these injury manifestations are produced, partially by the direct and prolonged UV-B and UV-A action on the skin cells and partially by the action mediated by the photoinduced free radicals (superoxide and hydroxyl) (Ayala, 1993).
The photoageing of the skin is a delayed effect that occurs in a more marked way in fair skin individuals.
Exposure to UV radiation and skin cancer
It is known that the UVR is capable of producing different damages on the DNA, such as:
genic mutations, chromatid exchanges, aneuploidy, etc and that these effects are or can be linked to the carcinogenesis.
Among the long term effects on the health, the induction of skin cancers is highly relevant both for amount and severity.
The analysis of the most recent scientific evidences shows that the ultraviolet (UV) radiation is one of the main causal factors for skin carcinomas (squamous cell carcinomas and basal cell carcinomas) and for skin melanoma, causes premature ageing of the skin and has harmful effects on health. Concerning the eye, the UV radiation can cause lesions and damages to the retina and the lens.
IARC classifies the solar spectrum of UV radiation and the tanning lamps as “carcinogens for humans” (1 A group ): this group includes substances and agents for which carcinogenicity to humans has been verified.
Concerning the use of indoor tanning facilities, we report the IARC (International Agency for Research on Cancer) statements, from the document "Sunbed use in youth unequivocally associated with skin cancer", 29 November, 2006 (that can be downloaded from this portal as a PDF):
''The data showed a prominent and consistent increase in risk for melanoma in people who first used sunbeds in their twenties or teen years: a 75% increase in risk of melanoma was calculated for such users of artificial tanning appliances, while this increase in the general population, although not statistically significant, is still not negligible. Artificial tanning confers little if any protection against solar damage to the skin, nor does use of indoor tanning facilities grant protection against vitamin D deficiency. Data also suggest detrimental effects from use of indoor tanning facilities on the skin's immune response and possibly on the eyes (ocular melanoma)''.
In this respects, ICNIRP recommends that ''If tanning devices are used, then the following specific recommendations (..) should apply: Claims of beneficial medical effects should not be made.''
The World Health Organisation (WHO-OMS) in the document Fact Sheet N°287 Interim Revision April 2010 states the following:
"Exposure to UV, either naturally from the sun or from artificial sources such as sunlamps, is a known risk factor for skin cancer. Short-wavelength UVB (280-315 nm) has been recognized for some time as carcinogenic in experimental animals, and there is increasing evidence that longer-wavelength UVA (315-400 nm) used in sunbeds, which penetrates more deeply into the skin, also contributes to the induction of cancer. A study conducted in Norway and Sweden showed a significant increase in the risk of malignant melanoma among women who had regularly used sunbeds. […] Aside from tanning, many people claim that use of sunbeds helps them to be more relaxed and have a feeling of wellbeing. It is difficult to quantify such claims. (...)
for the majority of the population, incidental exposure to the sun, combined with normal dietary intake of vitamin D, provides adequate vitamin D for a healthy body throughout the year. http://www.who.int/mediacentre/factsheets/fs287/en/
The UVR photoinduced carcinogenesis of skin cells is a long term multifactorial process that involves the body by local and systemic responses, including local and systemic immune response.
Skin carcinomas (basal cell and squamous cell carcinomas) are very frequent in humans; they show an increasing incidence with increasing age and occur most frequently in sun-exposed areas
The cumulative UV radiation exposure dose for a single individual correlates with the probability that the neoplastic event will occur, but does not basically influence its severity.
Skin melanoma is a very dangerous form of cancer whose incidence, as shown by the studies performed - in particular - in Australia an Israel, is related to UV exposure.
Generally, the individuals at the highest risk are white people, with fair skin and eyes, in particular those with blond and red hair with freckles and a large numbers of naevi.
Melanoma, unlike skin carcinomas, presents a poor correlation with cumulative radiant exposure of the individual: during life: occasional episodes of intense exposure that produce erythema, burns and vesicles, especially if occurred at young age, are considered causal factors that increase risk for the onset of this neoplasia.
UV radiation and immune system
Skin is a very complex organ and not a bare barrier that separates the external environment from the body. Inside it, an important part of the "peripheral arm" of the immune system resides and plays its function .
It has been observed that UVR exposure affects the immune response at local and systemic level, by suppressing both the humoral response, involving B-lymphocytes, and the cell-mediated response, involving T-lymphocytes.
It is not rare that, following an intense exposure to solar radiation, the typical lesions caused by herpes simplex virus appear in some individuals. It is thought that UVR exposure temporarily suppress the immune system, allowing the virus, present in the latent form, to multiply.
Phototoxic and photoallergic effects
UVR exposure and the contemporary intake of some chemical compounds can cause, in some individuals, photosensitization reactions that can occur with typical skin reactions. The skin photosensitization reactions are produced by:
1) photoallergic effects
2) phototoxic effects
There are several synthetic products (e.g. active ingredients of drugs) and natural products (plant extracts, cosmetic substances, perfumes) that can produce the above effects. It is important to underline that the UVRof the highest wavelength, in particular UV-A radiation, is efficient in inducing phototoxic and photoallergic reactions, because it penetrates more deeply and thus it is capable of interacting more easily with photoactive molecules (chromophores) taken by systemic administration and present in the peripheral microcirculation.
A laser is a device that allows to generate a monochromatic optical radiation, i.e. that it consists of essentially one extremely directional wavelength at high intensity . These features cannot generally be obtained by using incoherent light sources (e.g. incandescent lamps, LED, gaseous discharge lamps or arc lamps).
Even if they differ for the adopted technologies, all lasers are based on the same physical principle: coherent amplification of light intensity based on the stimulated emission of photons (Laser is the acronym for Light Amplification by Stimulated Emission of Radiation) and typically consist in an active material, whose physical properties determine the laser radiation wavelength, hold in a cylindrical container with two plane mirrors as a base.
Currently there is a wide variety of laser sources (solid-state, gas, organic dyes, excimer lasers) that cover a range of wavelengths including visible radiation, infrared and ultraviolet. Beyond lasers of the continuous wave (CW) type, there are lasers that emit pulses of high intensity and short duration (far beneath one picosecond).
Laser classification criteria
An important concept for defining the risk arising for the exposure to a laser apparatus it that of AEL (Accessible Emission Limit), that is defined as the maximum level of radiation from a source to which an operator can access and that determines the dangerousness of a laser product.
By studying the threshold for eye and skin damage according to the wavelength and the duration of the exposure to the laser radiation, the criteria for assigning a laser to a given class of danger have been deduced. They are based on the wavelength and on the AEL, i.e. on the power accessible to the operator .
The technical standard IEC EN 60825-1, concerning the safety of laser products, has been recently updated and, in the same time, the classification of the equipment has been revised. It is the responsibility of the manufacturer to provide correct classification of a laser product; starting from the 1st of July, 2005, any new device that is put into the market must be mandatorily compliant with the quoted updating (new classification).
Both for the old and for the new classification, the classes are determined on the basis of the AEL that describes the level of radiation emerging from a laser product, whose assessment allows to put the product in the correct hazard category. The AEL determination must be performed by the manufacturer in the worst possible condition for safety purposes. The classification of lasers indicates in ascending order their degree of dangerousness and the appropriate preventive and protective measures.
It is the responsibility of the manufacturer or his agent to provide correct classification of a laser product. If the user modify a product that has already been classified in such a way that this influences any aspect of the performances or the functions of the product, the person or the body that performs such a modification has the responsibility to guarantee the re-classification and the new marking of the laser product.
Thus, knowing its classification, it is possible to estimate the risk arising from the set up and use of the product.
Some examples of artificial optical radiation sources that entail a risk for the eyes and/or the skin for the individuals that are exposed to them are listed below
Electric arc (electric welding)
Electric arc weldings (excepting the gas ones), regardless of the metal, could exceed the limit values expected for UV radiation for a time of exposure in the order of tens of seconds, in the distance of one meter from the arc. The workers, the persons present or passing could be overexposed in the absence of adequate technical and organizational precautions.
Germicidal lamps for sterilisation and disinfection.
UVC emitted by the lamps are used to sterilize working areas and rooms in hospitals, food production plants and laboratories
Lamps for photo-hardening of polymers, photoengraving, "curing"
UV sources are usually located inside the appliances, but the possible radiation that can come out through openings or fissures is capable to exceed the limits in few tens of seconds.
“Black light” used in the non destructive test and control devices (except lamps classified in the “Exempt” group according to IEC EN 62471:2009)
Low – Medium or High depending to the application
The risk can be attributed to the UVA emission associated with visible radiation
UVA lamps are used in devices such those dedicated to the control and inspection of materials or to the control of banknotes; similar sources are used in entertaining places such as discotheques, pubs and concerts.
The systems used in metallurgy exceed the limit of exposure to UVA for times on the order of 1 - 2 hours, compared to activities that can be extended for the whole work shift.
Lamps/LED systems for phototherapy
UV radiation used for therapies in dermatology and the "blue light" used within the scope of health care activities (phototherapy of neonatal jaundice, refractive surgery, etc..).
Metal halide lamps
(High in case of direct vision)
They are used in theatres, in wide rooms (such as supermarkets) and in open settings for external lighting and can exceed both the limits for UV and for visible radiation, in particular for "blue light" by direct vision of the source.
(High in case of direct vision)
Possible overexposure to blue light by direct vision extended for more than 5-10 minutes: workers of car repair garages.
Scialitic lamps for operating theatre
(High in case of direct vision)
For some lamps the exposure limit values for blue light can be exceeded in 10 minutes in conditions of direct vision of the source
Metal halide lamps
They are used in theatres, in wide rooms (such as supermarkets) and in open settings for external lighting and can exceed both the limits for UV and for visible radiation, in particular for "blue light"
Medium – High
Sources used within aesthetic scope for tanning can emit both UVA and UVB, whose contributions vary on the basis of their typology. These sources exceed the limits for workers for exposures on the order of minutes.
Lamps for particular uses, excepted those classified in the “Exempt” group
Medium – High
These are fluorescent lamps not for general lighting, such as those used in acquaria or terraria.
These lamps present high UVB irradiances, that can lead to overexposures in few minutes, especially at close range.
General use lamps and special lamps classified in groups 1,2,3 according to standard IEC EN 62471:2009
Low-Medium-High depending on classification
LED systems included. Expedients are necessary for the set up and the safe use, if the class is above the first.
Incandescent bodies such as melted glass or metals, e.g. in the crucibles of the melting furnaces with incandescent body at sight, and their machining.
During the tap and in proximity of crucibles IRB and IRC exposures can exceed the limit values for times of exposure on the order of few seconds.
Lamp radiative heaters
Emissions of infrared radiations that exceed the upper limit values can be found at a distance of up to 2 meters from some radiative heaters: some expedients are necessary for the set up and the safe use.
Equipment with IPL sources for medical and aesthetic use
Emissions of optical radiation potentially much hier that the upper limit values even for few seconds Precautions are necessary for set up/safe use.
Very high/high: class 4/3B lasers; Medium: Class 2-3 lasers. Harmless: Class 1 lasers.
For Laser belonging to class 3B and 4 specific protection measures and specific set up requirements are mandatory for safety purposes.