The biological effects of different LED wavelengths in the health field. A review

Os efeitos biológicos de diferentes comprimentos de onda de LED na área da saúde. Uma revisão

Abstract

Introduction  the use of light emitting diodes (LED) in domestic and public vias have increased in the last 20 years. In addition, the LED light has been used as a light source for medical applications.

Objective  since humans are increasingly exposed to LEDs, there is an urgency to investigate the possible biological effects on tissues caused by this exposure. So, researchers have been focused their investigations in the application of this light in the health field.

Material and method  in this review, a search in important databases was performed on the biological effects caused after application of different LED light protocols in in vitro and in vivo studies.

Result  although most published papers have shown positive results, some of them reported negative biological effects of light LEDs technology on humans’ cells/tissues.

Conclusion  therefore, the comprehension of the biological effects caused by light LEDs will provide a better assessment of the risks involved using this technology.

Descriptors:
Phototherapy; light emitting diode; LED; light sources; LED biological effects

Resumo

Introdução  o uso de diodos emissores de luz (“LED”) em vias domésticas e públicas tem aumentado nos últimos 20 anos. Além disso, a luz LED tem sido usada para aplicações médicas.

Objetivo  pelo fato de seres humanos estarem cada vez mais expostos aos LEDs, há urgência em investigar os possíveis efeitos biológicos nos tecidos causados por esta exposição. Assim, pesquisadores têm focado suas investigações no uso desta luz na área da saúde.

Material e método  nesta revisão foi realizada uma pesquisa em bancos de dados conceituados sobre os efeitos biológicos causados após aplicação de diferentes protocolos de luz LED em estudos in vitro e in vivo.

Resultado  embora a maioria dos artigos publicados tenham mostrado resultados positivos, alguns deles relataram efeitos biológicos negativos da tecnologia de LEDs nas células/tecidos humanos.

Conclusão  portanto, a compreensão dos efeitos biológicos causados pela luz LED proporcionará uma melhor avaliação dos riscos envolvidos no uso desta tecnologia.

Descritores:
Fototerapia; diodo emissor de luz; LED; fontes de luz; efeitos biológicos do LED

INTRODUCTION

The search for safe and efficient energy devices has increased over the past 20 years, promoting major improvements in everyday use of equipment such as home appliances and electronics¹. The lamps are not the exception since the first incandescent lamps such as halogen and fluorescents had its energy efficacy improved¹. The light-emitting diode lamps (LED), have been commercialized with significant advantages over conventional devices, because of the internal energy-saving and lifetime that would compensate for the higher prices¹. Nowadays, the increasing public awareness of environmental concerns has pushed governments and supranational organizations to change the legislation, which regulates the electrical devices². As an example, it was reported that in the European Union, it was imposed a gradual withdrawal of incandescent lamps from the market by replacing them with LEDs (Regulation (EC) n° 244/2009)². In this context, in the future, people will become permanently exposed to LEDs, since these devices will illuminate their houses and the most public and private places. Soon, LED will comprehend at least 50% of the world lighting³. Thus, although humans are increasingly exposed to LEDs, the scientific community has been worried about the possible biological effects on tissues caused by this exposure. However, the number of studies performed are scarce.

In the last 15 years, due to a better understanding of photobiology and increased demand for minimally invasive and effective treatments, LEDs have been used for dermatological treatments¹,⁴. In the early 1990s, when NASA developed a LED device that allowed its first clinical application⁵, the biological effects of LEDs started to be identified¹. Then, several improvements have been introduced to LED devices resulting in equipment with different wavelengths. These devices have been investigated for their effects on skin cells and, while some studies report an increase in cell proliferation of fibroblasts and keratinocytes, others report disagreeing results on the clinical benefits of using LED on skin wounds⁶.

In a recent review, it was described that LED efficacy in photobiomodulation and others healthcare requests are well established and it may have therapeutic applications independent on the wavelength and protocol used⁷. In accordance with the ClinicalTrials.gov database, over 2800 scientific clinical investigations have been made focusing on the possible physiological effects of LED on the most varied parts of the human body, such as brain injury, skin healing, facial rejuvenation, lipolysis, periodontal diseases, temporomandibular disorders, healing of diabetic ulcers, photobiomodulation of Autism Spectrum Disorders (ASD), allergy, and sleeping bruxism⁸.

Taken together, it seems that the most of published papers demonstrated positive results in using different protocols and wavelengths of LED on cells or tissues, and the clinical trials that have been made using this device reinforce the idea that LED may be a promising alternative to treat human disorders in the future. Our counterword to this argument is that there are investigations in which protocol and wavelength of LED used were harmful to tissues. For this reason, this review examines the biological effects caused after the application of different LED protocols in the health field. A summary of protocols and wavelengths used is presented in Table 1.

Table 1
Summary finds of data extraction from included articles in the review

LED	Wavelength	Protocol	Associated biological effects	References
RED	630nm	3 applications at fluence of 8J/cm2	Stimulate the human collagen	Barolet et al., 20109
	647nm	applied for 10 s, 30 s or 90 s at fluences of 0.093J/cm2, 0.279J/cm2 and 0.836J/cm2	Osteogenic differentiation	Kim et al., 200910
	633nm	1 application at fluence of 0.5, 1.0, 1.5 and 2.0 J/cm2	Effect in human marrow stromal fibroblast cells: altered the gene expression related to cell proliferation, osteogenic potential, adipogenesis, mRNA and protein content.	Guo et al., 201511
	633nm	2 sessions a week for 4 weeks – 126J/cm2	Skin and mucosal wound healing, skin rejuvenation	Lee et al., 200712
	670nm	Daily treatment for 14 days using a fluence of 4 J/cm2	Treatment of precancerous lesions, warts, pain attenuation of oral mucositis	Whelan et al., 200213
	645nm	3 times a day for 1 week at fluence of 0.99 J/cm2	Relief in the oral mucositis	Corti et al., 200614
	660nm	5, 6 or 10 sessions for 1 to 3 weeks using a fluence of 5J/cm2	Treatment of polymorphous light eruption	Barolet, Boucher, 200815
	660nm	3 applications a week for 4 weeks (fluence not mentioned)	Skin rejuvenation	Barolet et al., 200916
	660nm	1 session a day for 12 weeks using a fluence of 5.17J/cm2	Treatment of wrinkles	Nam et al., 201717
	660nm	1 session at fluence of 10 J/cm2 for 7 days	Induction of angiogenesis	Sousa et al., 201318
Blue	412, 419 and 426 nm	66 to 100 J/cm2	Inhibited skin keratinocytes proliferation and altered cell differentiation	Liebmann et al., 201019
	430-490nm	Applications for 20, 40, 80 and 120 s at a fluence of 8, 14 and 15J/cm2	Reduction of mitotic activity of dermal fibroblasts	Malčić et al., 201220 and Lev-Tov et al., 201321
	420nm	15 and 30J/cm2	Decrease cell differentiation of dermal fibroblasts	Taflinski et al., 201422
	411nm	Fluence not mentioned	Apoptosis of human retinal cells	Knells et al., 201123
	465nm	10 min/day for 5 days at fluences of 9 and 18J/cm2	Apoptosis of human colon cancer cells	Matsumoto et al., 201424
	470nm	72 J/cm2, 144 J/cm2, 216 J/cm2 and 288 J/cm2	Reduced human colorectal cancer cells	Yan et al., 201825
	Not mentioned	162 J/cm2	Inhibited of gingival fibroblast proliferation	Taoufik et al., 200826
	Not mentioned	198J/cm2 for 72 h	Apoptosis of intestine cells of neonatal rats	Tanaka et al., 200827
	460nm	1 session at fluence of 10 J/cm2 for 7 days	Did not induce angiogenesis	Sousa et al., 201318
	400-500nm	Patients were exposed for at least 12 h. Fluence not mentioned	DNA damage of mononuclear leukocytes and decreased the blood flow in blood vessels in jaundiced neonates	Benders et al., 199928 Aycicek, Erel, 200729
	400nm	Light intensity of 200 Lux for 10 seconds	Damage on retinal cells	Ortín-Martínez et al., 201430
	455-465nm	Light intensity of 500 Lux	Damage on retinal cells	Krigel et al., 201631
	460nm	Light intensity of 150 Lux for 3h per day for 21 days	Toxicity for retinal pigment epithelial cells	Lin et al., 201932
	455-495nm	Review	Retina damage	Tosini et al., 201633
	455-495nm	Review	Inhibition of superoxide dismutase and catalase. Toxicity for retinal pigment epithelial cells	Tokarz et al., 201334
Yellow	570-590 nm	250 milliseconds at fluence of 0.1 J/cm2 for 4, 8, 12, 18 weeks and 6 and 12 months	Collagen synthesis, skin texture improvement	McDaniel et al., 200235 and Weiss et al., 200536
	570-590 nm	100 pulses, 250 milliseconds per pulse at fluence of 0.15 J/cm2	Decrease the incidence of dermatitis	DeLand et al., 200737
	590 nm	0.1 J/cm2	Increased collagen I production and decreased collagenase (MMP-1)	McDaniel et al., 201038
White	411-777 nm	CCTs equivalent to 2954, 5624, and 7378 K for 8h/16h	Toxic for lens epithelial cells	Xie et al., 20143
	411-777 nm	Illumination of animals with 6000 lux, 1500, 1000 and 500 lux for 1 week and 1 month	Toxic for lens epithelial cells	Krigel et al., 201631
	411-777 nm	Illumination of animals at constant light for 6, 12, 18, 24, 48, and 72 h	Toxic for retinal cells, loss of photoreceptors and the activation of caspase-independent apoptosis, necroptosis, and necrosis	Jaadane et al., 201539
	411-777 nm	5.17 J/cm2	Improved periocular wrinkles	Nam et al., 201740

• min: minutes; seg: seconds; h: hour.

Red LED - 630-700 nm

In accordance with the literature, the red LEDs (630-700 nm) are known to permit the penetration of light deeper into tissues when compared to other LEDs with different wavelengths, so, they are used to reach adjacent skin structures and also the connective tissue⁴¹. For this reason, the search for protocols that allow the treatment of the most varied health problems has been the target of some investigations⁹-¹¹. It has been reported that three applications of short and intermittent light delivery (red LED (630 nm) at a light dose of 8 J/cm², seems to stimulate the human collagen production in vitro⁹. In another investigation, it has been reported that red light, when used at 647 nm wavelength, applied for 10 s, 30 s or 90 s at light doses of 0.093 J/cm², 0.279 J/cm² and 0.836 J/cm², respectively, may promote the osteogenic differentiation in mesenchymal cells¹⁰. In addition, it has been reported that red LED (633 nm) altered the gene expression related to cell proliferation, osteogenic potential, adipogenesis, mRNA and protein content, in human marrow stromal fibroblast cells when irradiated at a light doses equivalent to 0.5, 1.0, 1.5 and 2.0 J/cm²,¹¹.

In the clinical field, many protocols for using red LEDs devices have been studied including skin and mucosal wound healing, skin rejuvenation¹², treatment of precancerous lesions, warts, pain attenuation of oral mucositis¹³, postoperative pain and edema⁴². Corti et al.¹⁴, using a red LED device (645 nm) with an output delivery equivalent to 7.8 mW/cm² and a dose of light of 0.99 J/cm², three times a day for 1 week, observed a relief in the oral mucositis present in patients underwent to chemotherapy¹⁴. Another investigation reported the efficacy of phototherapy using red LED (660 mn) in the treatment of polymorphous light eruption (PLE). The patients presented a reduction in the skin erythema, after 5, 6 or 10 sessions of treatment during 1 to 3 weeks. It was used equipment with an output delivery of 60 mW/cm² and a dose of light equivalent to 5 J/cm²,¹⁵. Barolet et al.¹⁶ demonstrated that the red LED at 660 mn can be a good choice to promote skin rejuvenation using in vitro and in vivo evaluation. In the in vitro assay, the authors used a Human Reconstructed Skin tissue (HRS) and applied 11 sequentially pulsed treatments of red LED for 4 weeks. For the in vivo study, patients received 12 applications of red LED being 3 treatments a week, for 4 weeks. Authors suggested that improvements in the skin of patients are justified by the upregulation of the collagen and downregulation of MMP-1, a gene encoding interstitial collagenase. However, details of the dose of light, time of application of each treatment and the output of the LED device were not mentioned¹⁶. Recently, a clinical trial was performed for the treatment of wrinkles. The faces of 52 female patients, were irradiated daily, with 5.17 J/cm² with red LED (660 nm) for 12 weeks and it was observed that red LED was the most successful protocol when compared to the LED wavelengths equivalent to 411 nm and 777 nm¹⁷. Additionally, it has been reported the capacity of red LED to induce angiogenesis on dorsal wounds after illumination, using a device with 15 mW and light dose of 10 J/cm² in rats. The protocol was applied once a day for 7 days and it promoted a significant increase in angiogenesis¹⁸.

The photobiomodulation therapy offers a non-invasive, safe, drug-free, and side-effect-free method for pain relief of both acute and chronic musculoskeletal conditions as well as fibromyalgia⁴³. When a super-pulsed laser (905 nm) combined with red (640 nm) and infrared (875 nm) light-emitting diodes, was used, it was observed that pain intensity decreased significantly, with a median decrease of 2.2 - 2.7 pain points on a 10-point scale and this decrease in pain was maintained for 48 h post treatment⁴⁴.

As can be seen, the protocols using red LED promoted a reduction of oral mucositis and skin lesions, increased angiogenesis and were efficient for skin rejuvenation. Besides, it has been reported an increase in cell proliferation of various cell types such as fibroblasts, endothelial cells, and keratinocytes. However, the biological mechanisms that justify the light actions of low intensity in tissues have not been elucidated.

Blue LED – 400-470 nm

It has been reported that the irradiation with blue LEDs (412, 419 and 426 nm) using a dose of light from 66 to 100 J/cm² inhibited the proliferation of skin keratinocytes and altered cell differentiation¹⁹. Likewise, in other investigations, dermal fibroblasts demonstrated reduced mitotic activity after exposure to blue LED (430-490 nm) for 20, 40, 80 and 120 seconds at a dose of light of 8, 14 and 15 J/cm²⁰,²¹. Taflinski et al.²², observed that human dermal fibroblasts exhibited a decrease in cell differentiation when irradiated with blue LED (420 nm), with an intensity of 50 mW/cm² and a dose of light of 15 and 30 J/cm². Human retinal cells have also been affected by blue LED irradiation²³. In an in vitro investigation, when human retinal cells were exposed to LED at 411 nm with an intensity of 0.6, 1.5 and 4.5 W/m² and 470 nm with an intensity of 4.5 W/m² was verified a cytotoxic effect of LED at 411 nm with the intensity of 4.5W/m², which induced the retinal cells to apoptosis²³. In addition, it has been reported the anti-proliferative effect of blue LED in cancer cells of the human colon by induction of the extrinsic apoptotic pathway²⁴. Recently, another in vitro study reported that the blue LED (470 nm) used at doses of 72 J/cm², 144 J/cm², 216 J/cm², and 288 J/cm², reduced proliferation of human colorectal cancer cells²⁵.

In the dental field, the blue LED when applied with an intensity of 900 mW/cm² and a dose of light equivalent to 162 J/cm², inhibited the proliferation of gingival fibroblasts²⁶. In another study, the blue LED was also applied to verify the viability and synthesis of dentin matrix proteins by odontoblast-like cells. The protocol used consisted in a single application using equipment with an intensity of 20 mW/cm and a dose of light equivalent to 0.5, 2, 4, 10, or 15 J/cm² and it was observed that blue LED did not present bio stimulatory capacity on odontoblast-like cells⁴⁵.

In an in vivo study it was demonstrated that the blue LED device induced intestine cells of neonatal rats to apoptosis when applied in an intensity of 55 mW/cm² for 72 hours²⁷. Another in vivo investigation verified that the blue LED (460 nm) did not stimulate angiogenesis on dorsal cutaneous wounds. It was performed one application per day for 7 days using a device with an intensity of 22 mW and dose of light of 10 J/cm¹⁸. Moreover, some in vivo investigations reported the genotoxicity of blue LED to mononuclear leukocytes and decreased the blood flow in blood vessels in jaundiced neonates²⁸,²⁹,⁴⁶-⁵⁰.

Similarly, to other areas, the investigations about the effects of blue LED in the ophthalmology field have increased³⁰,³¹. An in vivo investigation reported the phototoxicity effect of blue LED (400 nm) on retinal cells of rats, using an intensity equivalent to 200 Lux for 10 seconds³⁰. In another investigation, it was observed that the blue LED (455-465 nm) may cause retinal toxicity in rats, after illumination of 500 Lux, which is the domestic classic light intensity³¹. An in vivo study revealed that blue LED at 460 nm, was toxic for retinal pigment epithelial cells³². The authors illuminated rats with an intensity of 150 Lux for 3 h per day for 21 days and verified that the light caused fundus damage, decreased total retinal thickness, and caused neuron transduction injury in the retina³². It has also been documented that the degeneration of the pigment epithelium under blue light is promoted by the accumulation of A2E (bis-retinoid N-retinyl-N-retinylidene ethanolamine), but this effect does not show significant disturbances⁵¹.

In general, while only one investigation reported the benefits of using blue LEDs, in the inhibition of mitotic activity of cancer cells of the human colon²⁴, other investigations observed that different protocols using this LED may cause apoptosis in intestine cells of rats²⁷ and human retinal cells³⁰-³². Regarding the retinal cells, it was demonstrated that independently on the protocol of illumination used, the association between blue light and chronic retinal degeneration was verified³³. Short-wavelength blue light (455 nm to 495 nm) is characterized as high-energy radiation in the visible spectrum and is easily transmitted to the lens, directly causing damage to the retina³³. In addition, it was also reported that blue light inhibited the activity of superoxide dismutase and catalase³⁴ and induced the retinal pigment epithelium cells to death³⁴. Exposure to artificial light at night is a new source of pollution, because it affects the circadian clock and consequently, the secretion of melatonin and estrogen⁵². This topic is an important issue and needs to be emphasized since people are daily exposed to this type of light in their electronic products such as smartphones, tablets, and computers⁵²,⁵³.

Yellow LED 570-590 nm

Beyond the red and blue LEDs, previous investigations have reported the photobiomodulation caused by Yellow LED (570 - 590 nm)³⁵,³⁶. In these investigations, several protocols were developed, and the authors verified that the collagen synthesis was related to the clinical alterations found in human skin, including a lower production of some metalloproteinases³⁵. Based on the results, one protocol was defined (irradiations of 250 milliseconds with a dose of light of 0.1 J/cm² and the output delivery of 4.0 mW/cm²) and used for 4, 8, 12, 18 weeks and 6 and 12 months. The authors observed the improvement of the skin texture of 90 patients treated with yellow LED³⁶. In another study, it was observed that the photobiomodulation caused by yellow LED was efficient to decrease the incidence of dermatitis in patients with breast cancer³⁷. The patients were treated by application of 100 pulses, 250 milliseconds per pulse at a dose of light of 0.15 J/cm²,³⁷. McDaniel et al.³⁸, to upgrade the achieved clinical results, conducted an in vitro investigation combining the yellow LED with infra-red LED (590/870 nm). The output delivery used was equivalent to 4.0 mW/cm² and the dose of light was equivalent to 0.1 J/cm ². Authors observed a significant increase in collagen I and decrease in collagenase³⁸. When the LED (590 nm) was evaluated in cells, it inhibited human microvascular endothelial cells migration, vascular endothelial growth factor and stem cell factor, being a novel therapeutic option for treat melasma⁵⁴. It is important to notice that, since this type of light has photobiomodulation activity on human tissues, the number of investigations that used the yellow LED is scarce. Therefore, since these treatments yielded relevant results, further studies are necessary to clarify the effect of yellow LED on biological tissues.

White LED 411-777 nm

The photobiological effects of white LED on human cells were also evaluated³ and considering the optical characteristics, white LEDs may be quite diverse due to the different manufacturing techniques of the equipment. As a better description of the spectral characteristics of the white LED, the photobiological effects of the correlated color temperature (CCT) of white LED on cultured human corneal epithelial cells has been evaluated. Cells were irradiated with white LED with CCTs equivalent to 2954, 5624, and 7378 K. The irradiation was performed for 8 h/16 h, to mimic our daily routine. The results showed that LEDs increased the production of intracellular ROS and were genotoxic, both in a dose-dependent manner. Thus, white LED toxicity for lens epithelial cells was also directly dependent CCT³. In another investigation, commercially available white LEDs and four different blue LEDs (507, 473, 467, and 449 nm) were used for exposure of retinal cells of rats. Animals were exposed to constant light for 6, 12, 18, 24, 48, and 72 h, and it was verified a loss of photoreceptors and the activation of caspase-independent apoptosis, necroptosis, and necrosis³⁹. A recent report demonstrated that the blue component of white-LED caused retinal toxicity in albino rats⁴⁰. These results were observed after 24 hours of exposure at different light intensities (6000 lux, 1500, 1000 and 500 lux)³¹. In contrast, white LED (411-777 nm) when applied at a dose of light of 5.17 J/cm² was able to improve the periocular wrinkles of female patients⁴⁰. The oxidative stress activates multiple signaling pathways including mitogen-activated protein kinase cascades that are responsible to causes retinal pigment epithelium damage⁵⁵.

As commented previously, the blue component of white light seems to be the main responsible for its toxicity. Taking into consideration that white LED is the most used light in domestic lighting, public and private roads, their widespread use needs to be reassessed.

The Action of LEDs on Cells

In general, it has been suggested that the cytotoxicity of LEDs is related to the increase of cell apoptosis, production of reactive oxygen species (ROS), lipid peroxidation and DNA damage³,⁵⁵. Mitochondria have also been identified as a target for the toxicity of LED illumination¹⁵,²³,⁵⁶,⁵⁷, which could be related to the induction of apoptosis. It is known that the mitochondria, a fundamental organelle for maintaining vital cellular functions, also plays a key role in cell death through the regulation of cytochromes⁵⁸,⁵⁹, intracellular Ca²⁺ concentration⁵⁹, reactive oxygen species (ROS)⁶⁰-⁶², transmembrane mitochondrial potential⁶³, mitochondrial transition pores by caspases or ATP depletion⁶², changes in the redox state metabolism⁶⁴ and cyclosporine A-sensitive mitochondrial permeability transition⁶². The irradiation by LED is absorbed by mitochondrial chromophores, including cytochrome c oxidase¹. Irradiation affects the mitochondrial respiratory chain by changing the electrical power of cellular membranes and, consequently, the selective permeability of sodium, potassium, and calcium ions or through increased activity of enzymes, such as cytochrome c oxidase and ATP synthase⁶³,⁶⁵. In addition, it has been reported an increase in the mitochondrial respiration in the respiratory control state of rat liver cells, after irradiation with LED at 650 nm in a dose of 3 J/cm² or higher⁶⁶. On the other hand, the same research group found a decrease of mitochondrial respiration of rat liver cells, in the phosphorylating state, after irradiation using the same red LED and doses of light. They demonstrated that the cytochrome c oxidase is important in the photoreactivation of mitochondrial activity blocked by nitric oxide⁵⁷. Therefore, according to the results of these studies the alteration caused by LED on the mitochondrial level is still controversial.

Concerning the DNA damage, it is important to note that DNA damage would be expected as a consequence of mitochondrial impairment and ROS production caused by LED irradiation independently of the wavelength used²⁵. However, reports on genotoxicity are scarce and sometimes contradictory²⁵,⁵⁵,⁶⁷. Considering that these radiations may promote DNA modifications, they can become potentially mutagenic and cause malignancy in human cells, so, this aspect should be explored in the future. Moreover, the effects that LED may cause human cells is dependent on the wavelength, the intensity of the LED device, the distance between the equipment and the cells irradiated, energy delivered per surface area and the exposure time employed for each protocol used. Each color of light or wavelength presents different penetration depths on biological tissues, beyond each biological effect related to differences in chromophore targets⁴,⁶⁸.

Relevant Considerations

In the present review, it is important to mention the ICNIRP Guideline, 2013 (International Commission on non‐ionizing radiation protection), which describes the principles of protection against laser radiation hazards, in parallel to the exposure to non-laser optical radiation⁶⁹. In accordance with ICNIRP, shorter-wavelength visible radiation in the region from 400 nm to 550 nm (blue light region), has been suggested to damage the retina, for lasers and non-laser radiation⁷⁰-⁷². Thus, based in these observations one can assume that the harmful effects caused by LED radiation would be reproduced by laser radiation, just using the same power and wavelength of light. However, the guideline suggests that the safety limits of exposure for laser and non-laser sources, such as the sun, tungsten filaments xenon lamps, and LEDs, may be different⁶⁹. These differences might be related to the nature of each radiation, for instance, the controlled or non-controlled emission of photons and also the type of beam produced by the light source such as the case of the laser beam, which is well collimated, while LED beam is not collimated⁶⁹. As the exposure limits also depend on the irradiance diameter (spot size), a collimated beam is more conservative than the non-collimated counterpart, in the context of light safety exposure.

As for the emission spectrum, it has been reported that LED devices is constituted of blue radiations or blue components, known to be potentially dangerous to the retina. It was verified that the blue components cause retinal toxicity at occupational domestic illuminance and not only under experimental conditions³¹. So, the biological effects reported here, allow us to question the safeness of the LED radiation. It is possible to suggest that the effects produced by the LED devices, are related not only to the power or wavelength of LED device but also to the nature of the light radiation. Taking together, these arguments reinforce the idea that the nature of light can be another factor to cause adverse effects on biological tissues.

CONCLUSION

In summary, the phototherapy seems to be a promising alternative to treat a varied range of diseases. However, the results described in the literature are inconsistent, mainly due to the lack of methodological standardization of the studies. It is important to state that most investigations were performed based on acute light exposure and do not take into account the effects of prolonged exposures on timescales of weeks, months, and years to mimic human daily routine³¹,⁶⁹. Therefore, the comprehension of biological effects caused by repeated exposure of LEDs will provide a better assessment of risks involved using this technology. These data would be of extreme importance to manufacturers of light devices to improve the safeness and eliminate the harmful effects of LED irradiation.

ACKNOWLEDGMENTS

This work was supported by São Paulo Research Foundation (FAPESP), Brazil (grants numbers #2013/07276-1, #2016/13868-7 and # 2017/02559-6).

• How to cite: Carmello JC, Barbugli PA, Jordão CC, Oliveira R, Pavarina AC. The biological effects of different LED wavelengths in the health field. A review. Rev Odontol UNESP. 2023;52:e20230028. https://doi.org/10.1590/1807-2577.02823

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Publication Dates

• Publication in this collection
  27 Nov 2023
• Date of issue
  2023

History

• Received
  25 Oct 2023
• Accepted
  26 Oct 2023