Non-laser Light Source Research Articles

Public exposure to artificial optical radiation in the aesthetics and the entertainment sector in Greece. Risk management actions.

Safety issues are raised from the use of low- and high-power optical radiation sources, both laser and non-laser, by non-experts for aesthetic and entertainment purposes. The Greek Atomic Energy Commission relied on the ISO 31000:2018 framework to manage the public exposure risk to such cases. Risk was evaluated as (1) intolerable for lasers and intense pulsed light sources at aesthetic procedures and in the case of laser pointers, (2) severe for lasers at laser shows and (3) moderate for light-emitting diodes (LEDs) at aesthetic procedures, home-use intense pulsed light sources/LEDs and laser/LED projectors. Operators' training, public awareness campaigns, intensive market surveillance actions and the enhancement of the regulatory framework have been proposed as risk treatment/control measures and have been prioritised in this order, according to their effectiveness in reducing the exposure risk and their urgency of implementation. The Greek Atomic Energy Commission developed public awareness campaigns regarding exposure safety to laser and non-laser light sources at aesthetic procedures and the use of laser pointers.

Preliminary Monte Carlo simulation of non-laser light sources for photodynamic therapy

In photodynamic therapy (PDT), a photosensitizing agent is administered following irradiation on the target volume. The wavelength beam to activate the photosensitizer is ranging from 400 nm to 800 nm. Such wavelengths are generated by laser and non-laser light sources. However, the use of x-ray induced in photodynamic therapy has been investigated as a combination of radiotherapy and PDT. Moreover, x-rays are used for deeper penetration into tissue, extending the use of this therapy for tumours that would not be reachable by conventional PDT. In general, x-rays with keV to MeV energies are used for X-PDT. The aim of the present work is to investigate the use of monochromatic, low-energy beams for photodynamic therapy applications. Monte Carlo simulations are performed for distinct target volumes irradiated by a nonlaser (low-energy x-rays). Models of soft tissue and a mixture some photosensitizer plus soft tissue were considered. For each case, the energy fluence distribution at a given depth was calculated. A higher percentage difference of ∼20% was found when comparing the beam profile between soft tissue and the mixing Hpd, Photofrin, ALA, PpIX with soft tissue for low energy x-ray. Preliminary results showed that simulated x-ray beams could work for PDT.

Laser Influence on Dental Sensitivity Compared to Other Light Sources Used During In-office Dental Bleaching: Systematic Review and Meta-analysis.

The use of laser light during bleaching will not reduce the incidence or severity of sensitivity and will not increase the degree of color change compared with nonlaser light sources. Objective: To evaluate whether the use of laser during in-office bleaching promotes a reduction in dental sensitivity after bleaching compared with other light sources.Methods: The present review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) and is registered with PROSPERO (CDR42018096591). Searches were conducted in the PubMed/Medline, Web of Science, and Cochrane Library databases for relevant articles published up to August 2018. Only randomized clinical trials among adults that compared the use of laser during in-office whitening and other light sources were considered eligible.Results: After analysis of the texts retrieved during the database search, six articles met the eligibility criteria and were selected for the present review. For the outcome dental sensitivity, no significant difference was found favoring any type of light either for intensity (mean difference [MD]: -1.60; confidence interval [CI]: -3.42 to 0.22; p=0.09) or incidence (MD: 1.00; CI: 0.755 to 1.33; p=1.00). Regarding change in tooth color, no significant differences were found between the use of the laser and other light sources (MD: -2.22; CI: -6.36 to 1.93; p=0.29).Conclusions: Within the limitations of the present study, laser exerts no influence on tooth sensitivity compared with other light sources when used during in-office bleaching. The included studies demonstrated that laser use during in-office bleaching may have no influence on tooth color change.

Metastases from malignant melanoma after laser treatment of undiagnosed pigmented skin lesions

Brown spots and moles often give rise to cosmetic complaints and removal with lasers and non-laser light sources may seem advantageous. However, pigmented skin lesions comprise a diversity of lesions, some of which are well treated with lasers, i.e. benign epidermal lesions such as ephelides and lentigo benigna, and others for which laser exposure is controversial or even contradictory, i.e. melanocytic nevi, dysplastic nevi and malignant melanoma [1]. A recent publication has highlighted the need for careful evaluation of pigmented lesions prior to laser treatment due to the fact that distinguishing a benign lesion from other pigmented lesions can be difficult [2]. Laser treatment of melanocytic nevi remains controversial, since these may possess the potential of progressing into their malignant counterparts. That being said, various types of quality-switched pigment-specific and ablative lasers are used to lighten and remove melanocytic nevi [1–7]. In literature, case reports are presented on pseudo-melanoma, malignant melanoma and metastases after laser exposure of pigmented skin lesions [8, 9] and in vitro studies have shown altered expression of tumour suppressor (p16) gene and adhesion molecules in melanoma cell lines [10]. In May 2010, a 41-year-old Danish male visited a laser spa in Japan, requesting removal of four brown– black pigmented lesions on his left lower arm, armpit, neck and scalp. He entered directly from the street and no pre-appointment or medical referral was required. A therapist wearing a white coat inspected the lesions and offered to remove these with a laser device. Dermoscopy was not performed, neither were biopsies taken. Expenses for laser removal of the four pigmented lesions amounted a total of 10 EUR. The patient explained that treatment was initiated with infiltration anaesthesia and the laser exposure a burning procedure performed with a hand piece, from which intense red light was directed against the skin lesions leaving smoke generation. The procedure was followed by ulceration that healed after 7–10 days. Approximately 3 months after laser treatment, the patient noticed the emergence of skin eruptions on his left lower left arm. December 2011, 19 months after the laser exposure, he was referred to a dermatologist due to persistently growing tumours on his arm. On examination, the patient was fair skinned with moderate to severe dermatoheliosis. He had no family history of malignant melanoma, but received massive sun exposure from 12years of living in Thailand with only occasional use of sun protection. Tumours presented as three subcutaneous, firm nodules with a purple hue and two red, fleshy, protruding elements, involving an area of 7×5 cm. Solitary lesions were up to 1.5 cm in diameter (Fig. 1). Clinically, there were no palpable lymph glands. Dermoscopy showed no pigmentation pattern but a structure-less appearance with increased vascularisation and inflammation without epidermal changes. Skin biopsy showed a deeply located T. H. Larsen :M. Nielsen :R. Lindskov Private Practice of Dermatology, Panoptikon Banegaardspladsen 15, 1570, NV, Copenhagen, Denmark

Nebenwirkungen und Komplikationen in der Therapie mit Laser- und Lichtgeräten

The possible treatment errors and complications with the use of laser and non-laser light sources are presented along with corresponding preventive measures. Particular emphasis is laid on practice-related errors and how to avoid them. A checklist for the safe conduct of treatments using laser and non-laser light sources completes the article.

Monte Carlo simulations for optimal light delivery in photodynamic therapy of non-melanoma skin cancer

The choice of light source is important for the efficacy of photodynamic therapy (PDT) of non-melanoma skin cancer. We simulated the photodynamic dose (PDD) delivered to a tumour during PDT using theoretical radiation transfer simulations performed via our 3D Monte Carlo radiation transfer (MCRT) model for a range of light sources with light doses up to 75 J cm−2. The PDD delivered following superficial irradiation from (A) non-laser light sources, (B) monochromatic light, (C) alternate beam diameters and (D) re-positioning of the tumour within the tissue was computed. (A) The final PDD deposited to the tumour at a depth of 2 mm by the Paterson light source was 2.75, 2.50 and 1.04 times greater than the Waldmann 1200, Photocure and Aktilite, respectively. (B) Tumour necrosis occurred at a depth of 2.23 mm and increased to 3.81 mm for wavelengths 405 and 630 nm, respectively. (C) Increasing the beam diameter from 10 to 50 mm had very little effect on depth of necrosis. (D) As expected, necrosis depths were reduced when the tumour was re-positioned deeper into the tissue. These MCRT simulations show clearly the importance of choosing the correct light source to ensure optimal light delivery to achieve tumour necrosis.

Programmable Illumination and High-Speed, Multi-Wavelength, Confocal Microscopy Using a Digital Micromirror

Confocal microscopy is routinely used for high-resolution fluorescence imaging of biological specimens. Most standard confocal systems scan a laser across a specimen and collect emitted light passing through a single pinhole to produce an optical section of the sample. Sequential scanning on a point-by-point basis limits the speed of image acquisition and even the fastest commercial instruments struggle to resolve the temporal dynamics of rapid cellular events such as calcium signals. Various approaches have been introduced that increase the speed of confocal imaging. Nipkov disk microscopes, for example, use arrays of pinholes or slits on a spinning disk to achieve parallel scanning which significantly increases the speed of acquisition. Here we report the development of a microscope module that utilises a digital micromirror device as a spatial light modulator to provide programmable confocal optical sectioning with a single camera, at high spatial and axial resolution at speeds limited by the frame rate of the camera. The digital micromirror acts as a solid state Nipkov disk but with the added ability to change the pinholes size and separation and to control the light intensity on a mirror-by-mirror basis. The use of an arrangement of concave and convex mirrors in the emission pathway instead of lenses overcomes the astigmatism inherent with DMD devices, increases light collection efficiency and ensures image collection is achromatic so that images are perfectly aligned at different wavelengths. Combined with non-laser light sources, this allows low cost, high-speed, multi-wavelength image acquisition without the need for complex wavelength-dependent image alignment. The micromirror can also be used for programmable illumination allowing spatially defined photoactivation of fluorescent proteins. We demonstrate the use of this system for high-speed calcium imaging using both a single wavelength calcium indicator and a genetically encoded, ratiometric, calcium sensor.

61 Combination of rectangular pulsed ER: YAG and ND: YAG laser treatments for skin ageing signs correction

: Photodynamic therapy involves the activation by visible light of a previously administered photosensitizing agent in order to cause tumor necrosis. Skin tumors can be treated with topical photosensitizers and thus avoiding systemic side effects. In this study we evaluate the immediate and long-term effects of photodynamic therapy (PDT), using aminolevulinic acid (ALA) as a photosensitizer and a non-laser light source, on Bowen's disease (intra-epithelial squamous cell carcinoma) and on frank squamous cell carcinoma (SCC) of the skin.ALA in cream form (20%) was topically applied on biopsy-proven Bowen's disease or SCC of the skin. The lesions were covered with occlusive and light-shielding dressing. Sixteen hours later, they were submitted to a 10-min light session using Versa-Light™, a non-laser light source (spectral output of 580–720 nm and 1250–1600 nm, 100 J/cm2). The initial evaluation was done 21 days post-treatment and every 3 m thereafter. Patients that did not respond to treatment after two to three sessions were referred to surgery.Forty Bowen's disease lesions (24 patients) and 43 SCC lesions (18 patients) underwent treatment. Median follow-up was 21 ± 8 m. No patient had any remarkable side effects. Thirty-four Bowen's disease (85%) lesions completely responded as did 32 SCC lesions (74%).: Our findings showed that PDT is highly effective in treating Bowen's disease and SCC lesions and can be used as a first treatment modality in so far as its use does not preclude the subsequent surgery recommended for the small percentage of failures.

Lentigines, laser, and melanoma: A case series and discussion

Solar lentigines are considered one of the earliest signs of photoaging and are an extremely common cosmetic complaint. Successful removal of these lesions can be achieved with laser and non-laser light sources, and is one of the most frequently performed cosmetic procedures in laser centers. Distinguishing a benign lentigo from other pigmented lesions can sometimes be challenging, even for a trained dermatologist. We report a series of three patients who presented to our laser center within 2 months of one another for cosmetic removal of pigmented lesions that were found to be melanoma. One patient was referred by another dermatologist, one by a physician family member, and the other presented on his own. These cases highlight the need for careful evaluation of pigmented lesions prior to laser treatment, regardless of the source of the referral. In this article, we will review the diagnostic and treatment differences between lentigines and their malignant counterparts, and examine the role of laser in both.

Actively coupled cavity ringdown spectroscopy with low-power broadband sources.

We demonstrate a coupling scheme for cavity enhanced absorption spectroscopy that makes use of an intracavity acousto-optical modulator to actively switch light into (and out of) a resonator. This allows cavity ringdown spectroscopy (CRDS) to be implemented with broadband nonlaser light sources with spectral power densities of less than 30μW/nm. Although the acousto-optical element reduces the ultimate detection limit by introducing additional losses, it permits absorptivities to be measured with a high dynamic range, especially in lossy environments. Absorption measurements for the forbidden transition of gaseous oxygen in air at ∼760nm are presented using a low-coherence cw-superluminescent diode. The same setup was electronically configured to cover absorption losses from 1.8×10-8cm-1 to 7.5% per roundtrip. This could be of interest in process analytical applications.

NEW CLASSIFICATION FOR SINGLE-SYSTEM LIGHT TREATMENT

Although the use of the laser in medical applications has increased dramatically during the last three decades, it is significant that during the last few years non-laser light sources have gained prominence in photomedicine and photosurgery, particularly the use of light-emitting diodes (LEDs) and intense pulsed light (IPL). The author therefore believed it was important to devise a new classification of light/tissue interactions, and that the well-accepted acronym LLLT and HLLT should now stand for low level light therapy and for high level light treatment, since the 'L' in 'laser', LED and IPL stands for 'light'. The author herein presents a classification, which is based on the level of reaction induced by the light incident on tissue, rather than being based on the system used to deliver the light energy. When the level of tissue reactivity to light of very low incident power and energy densities is well below the cells' damage threshold, so that instead of being damaged the cells are directly activated by the low incident photon density, the changes in the irradiated tissue are photoactivative and reversible: the author hereafter refers to this group of reactions as low level light therapy (LLLT). When the level of tissue reactivity to light of very high incident power and energy densities is over the cells' damage threshold, so that the cells are directly destroyed, the changes in the irradiated tissue are photodestructive and irreversible: the author hereafter refers to this group of reactions as high level light treatment (HLLT). For levels of tissue reaction intermediate to HLLT and LLLT, the author suggests the new term, medium level light treatment (MLLT), as described in detail herein. When the new classification system of light treatment (LT) is understood and used, the author feels this offers an accurate and simple method of classifying light/tissue reactions by the therapeutic reaction itself, rather than by the light source, laser, LED, IPL system or other, used to produce the reaction.

Monitoring the Granulomal Micro-environment in a Monkey Model of Tuberculosis Using a Novel Fluorescence Bronchoscope

Tuberculosis is a disease that infects one in three humans today. The long, expensive drug course required to cure the active form, combined with its increasing resistance to conventional antibiotic treatment, necessitates the development of a new class of TB drugs. To evaluate the efficacy of these drugs, as well as to gain increased basic knowledge of the disease's progression, we are building a novel 0.8 mm diameter bronchoscope as part of a multi-institutional initiative to develop a primate-based tuberculosis model system. In order to monitor the in vivo microenvironment of the tuberculosis granuloma, monkeys will be inoculated with transgenic pH reporting tuberculosis bacilli and GFP expression measured to quantify the local pH and other micro-environmental parameters. CT scans will be used to reveal the induced nodules/lesions and guide the bronchoscope to the granulomas. The lung tissue itself contains many 488 nm excitable endogenous fluorophores (e.g. elastin, collagen) and autofluorescence limits the level of reporter quantification. To overcome this problem we are employing a photoactivatable protein (Dronpa) as the reporter expressed by the bacteria. Using a novel pulsed UV/Blue non-laser light source, the protein's fluorescence can be modulated to distinguish reporter signal from the constant autofluorescence background and therefore produce highly quantitative measurements of changes in the granuloma microenvironment during the progression of the disease and during drug treatment.(Supported by the Gates Foundation and NIH/NIBIB P41 RR04224 to WRZ.)

Molecular mechanisms of photochemotherapy (Review)

Mechanisms of photophysical, photobiological, and therapeutic action of light on blood in vivo are discussed based on results of spectral and clinical studies of blood, plasma, and erythrocytes. Spectral manifestations of photochemical reactions initiated in blood by therapeutic doses of radiation in vivo with light of different wavelengths are considered. Spectral and clinical results of blood investigations are compared for patients whose complex treatment included intravenous blood irradiation and magnetotherapy. Mechanisms for secondary (dark) reactions induced by the action of light on blood in vivo are discussed. The radiation of laser and non-laser light sources used at present for intravenous blood irradiation (365, 405, 450, 530, 632, 635, 808 nm) is shown to fall within hemoglobin absorption bands. The conclusion is made that blood absorption of laser and non-laser light radiation results in functional alteration of hemoglobin as a possible primary photoacceptor absorbing light radiation of the above wavelengths. The therapeutic effect of intravenous blood irradiation is initiated by hemoglobin functional activity modulation. Phototherapy is a means to correct it. Intravenous phototherapy should be considered as a therapeutic method that changes (provided that the dosage is correct) the balance of active oxygen species production and their inhibition by antioxidants.

Photodynamic Therapy for Urological Malignancies: Past to Current Approaches

Modern PDT for urological tumors is a potentially selective approach in which in situ photosensitization by a nontoxic drug, locally activated by light, generates cytotoxic reactive oxygen species, causing cell death. While urological clinical experience with PDT is largely limited to treatment for superficial bladder cancer, the advent of novel photosensitizers and technologies for treatment planning, light delivery and dosimetry, PDT for prostate and other urological cancers appears increasingly realistic. We reviewed the current literature on PDT for urological tumors, in addition to recent emerging data from our laboratory and elsewhere. Remarkable progress has been made in the field of photochemistry and photobiology. Together with improved optical delivery and imaging systems PDT holds promise as an alternative, minimally invasive and potentially curative treatment for localized solid tumors as well as for palliative treatment for isolated, clinically problematic metastases. Current experience with photodynamic therapy using contemporary photosensitizing agents and light sources is mainly restricted to in vivo experimental models and early phase clinical trails. However, ongoing preclinical work and clinical trials indicate that safer and effective PDT treatments in uro-oncology are imminent.

Lattice of optical islets: a novel treatment modality in photomedicine

A majority of photothermal applications of laser and non-laser light sources in medicine (in particular, in dermatology) are based on the paradigm of (extended) selective photothermolysis. However, realization of this principle in its strict form may not always be possible and/or practical. Spatial (or geometric) selectivity (as opposed to wavelength and temporal selectivity) can provide an alternative approach delivering effective and safe treatment techniques. A method of creating a lattice of localized areas of light–tissue interaction (optical islets) is an example of this ‘spatially confined’ approach. The lattice of optical islets can be formed using a variety of energy sources and delivery optics, including application of lenslet arrays, phase masks and matrices of exogenous chromophores. Using a state-of-the-art theory of optical and thermal light–tissue interactions and a comprehensive computer model of skin, we have conducted a theoretical and numerical analysis of the process of formation of such a lattice in human tissue. Effects of the wavelength, beam geometry, pulsewidth and physical properties of tissues have been considered. Conditions for obtaining optical, thermal and damage islet lattices in the human skin without inducing adverse side effects (e.g. bulk damage) have been established.

Construction and evaluation of a non-laser optical system for photodynamic process excitation

Purpose: To show that a non-laser light source can be constructed, using a 500 W Tungsten lamp and optical filters, and that this light source produces photodynamic effect via protoporphyrin IX (PpIX) similar to the effect produced by HeNe laser light. Methods: The broad band spectrum from a Tungsten lamp was filtered. Infrared and blue part of the spectrum was discarded by absorption process and the fraction of the spectrum, centered at the red portion, was filtered by an interference filter. Photodynamic effect was studied by the activity on endogenous PpIX of Harderian glands of Wistar rats. Twenty rats were used for the experiment. Each animal had its two Harderian gland surgically exposed, so one of them was treated with the system while the other was kept as control. After a 30 minutes period of treatment, the animals were sacrificed and their glands were removed for histological analysis. This analysis was compared to earlier published results obtained with HeNe laser light. Results: The resultant light source emission was centered around (636 ± 6.5) nm and gives up to 11.3 mW/cm² power density. It produces photodynamic effect in Harderian gland, observed either by fluorescence spectroscopy or by histological microscopy. Conclusion: There is no noticeable difference in Photodynamic effect results if activated by HeNe laser or by the proposed non-laser light source emitting at the red portion of the spectrum.

Photodynamic therapy for Bowen's disease and squamous cell carcinoma of the skin

Photodynamic therapy involves the activation by visible light of a previously administered photosensitizing agent in order to cause tumor necrosis. Skin tumors can be treated with topical photosensitizers and thus avoiding systemic side effects. In this study we evaluate the immediate and long-term effects of photodynamic therapy (PDT), using aminolevulinic acid (ALA) as a photosensitizer and a non-laser light source, on Bowen's disease (intra-epithelial squamous cell carcinoma) and on frank squamous cell carcinoma (SCC) of the skin. ALA in cream form (20%) was topically applied on biopsy-proven Bowen's disease or SCC of the skin. The lesions were covered with occlusive and light-shielding dressing. Sixteen hours later, they were submitted to a 10-min light session using Versa-Light™, a non-laser light source (spectral output of 580-720nm and 1250-1600nm, 100J/cm(2)). The initial evaluation was done 21 days post-treatment and every 3m thereafter. Patients that did not respond to treatment after two to three sessions were referred to surgery. Forty Bowen's disease lesions (24 patients) and 43 SCC lesions (18 patients) underwent treatment. Median follow-up was 21±8m. No patient had any remarkable side effects. Thirty-four Bowen's disease (85%) lesions completely responded as did 32 SCC lesions (74%). Our findings showed that PDT is highly effective in treating Bowen's disease and SCC lesions and can be used as a first treatment modality in so far as its use does not preclude the subsequent surgery recommended for the small percentage of failures.

Photodynamic-induced vascular damage of the chick chorioallantoic membrane model using perylenequinones.

The chorioallantoic membrane (CAM) assay is a widely used bioassay in early in vivo cancer research. The CAM allows non-invasive study of in vivo microvasculature and blood circulation. This report describes the first topical application investigation of photodynamic response in the CAM model using Hypericin (HY) and Hypocrellin B (HB) that belongs to the perylenequinone family. Briefly, cultivated carcinoma of the human bladder cell line (MGH), were inoculated on the CAM of fertilized eggs of embryo age (EA) 9. Tumor growth was evaluated by digital stereomicroscopy. Photodynamic therapy (PDT) was performed following topical application of the photosensitizers. We were able to demonstrate that these perylenequinones localized selectively in the xenografted bladder tumor and in the vasculature of the CAM. Photodynamic treatments were performed using a custom-made non-laser light source coupled into a flexible fiber bundle to selectively excite the photosensitizers in order to induce photodamage to the tumor and vasculature. The vascular damage induced was quantitatively measured following topical application of the photosensitizers. Both photosensitizers exhibited very similar degrees of photodamage to the CAM. The CAM model offers an exciting avenue for the study of PDT induced effect on the vasculature. Our preliminary results support that the CAM model could potentially serve as a customized model to study photodynamic therapy effects of various photosensitizers on specific tumor models.

Efficacy of Different UV‐emitting Light Sources in the Induction of T‐cell Apoptosis¶

ABSTRACTUltraviolet B(UV‐B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV‐B immunosuppression in this treatment modality is thought to be an apoptosis‐inducing effect on T cells infiltrating the skin. We examined the T‐cell apoptosis induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis‐inducing capacity of different UV‐B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV‐B light for the induction of T‐cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis‐inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.

Efficacy of different UV-emitting light sources in the induction of T-cell apoptosis.

Ultraviolet B (UV-B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV-B immunosuppression in this treatment modality is thought to be an apoptosis-inducing effect on T cells infiltrating the skin. We examined the T-cell apoptosis-induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis-inducing capacity of different UV-B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV-B light for the induction of T-cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis-inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.