**2. Red light transcranial LED therapy (RL-TCLT): types, devices, uses, and effects**

The use of transcranial photobiomodulation is promising in therapeutic and medical benefits for health, with increasing application and projection also in aging and neurodegenerative diseases [9, 24, 25]. The light presents different characteristics that could be used advantageously in the field of health, principally by recent

lighting technologies based on an extensive range of diverse light sources, that have been used for photobiomodulation [8]. Light for therapeutic purposes corresponds to a small fraction of the spectrum of luminous radiation, generally in the visible spectrum [8, 25], where it has a biological effect based on the premise of mammalian cellular metabolism from photoreceptors and chromophores molecules [25].

Diverse devices have been used, including Light Amplification by Stimulated Emission of Radiation (Laser) devices, Low-level light laser therapy, and lightemitting diodes (LED) devices [26]. LED devices are semiconductors that present a high efficiency of electrical energy conversion into optical energy, dissipating little thermal energy [26]. Furthermore, these devices can have widely fluctuating power levels depending on the size, number, and power of the individual diodes [16, 27, 28]. LED devices have been compared with lasers; however, devices irradiating LED are bandwidth (approx 40 nm), beam divergence, incoherent radiation emission, and high optical output power; favoring the absorption of energy by different molecular structures [5, 8]. In addition, LED devices have been considered as a safety by the US Food and Drug Administration (FDA) [29].

Red-Light Transcranial Led Therapy (RL-TLTC) involves power-efficient, low heat-producing light sources that have the potential to deliver high-intensity RL of 600-690 wavelengths, that can be pulsed or continuous [30]. In this therapy, the light goes through the layers of the skin and skull, to stimulate the brain and specific cerebral regions, causing biological responses that result in benefits for the individual [7, 8, 31]. In particular, RL-LED mediated a vibrational absorption process, which produces a photochemical effect that leads to the absorption of photons by specific molecules in the cell [5]. In addition, the wavelength (nm), energy density (J/cm2 ), and power density (mW/cm2 ) are parameters that determine the effectiveness of RL-TLTC. The wavelength of light used is critical since not all ranges of light used have a similar effect, some ranges present reduced effects such as wavelength in the 700–750 nm range. In contrast, RL-LED at 600–690 nm or 760–900 nm has more impact on the biological tissues [5, 8]. Considering that these parameters of light radiation interact with biological tissue, they cause optical phenomena of reflection, transmission, propagation, and absorption. These characteristics also can present variations depending on tissue irradiated, for example by different concentrations of photoreceptor and chromophores molecules that contain biological tissues, like water, cytochromes, and organic molecules as flavins, hemoglobin, and melanin, among others [5]. When light is absorbed, the photon energy reaches the target molecules producing vibrational, rotational, or electronic processes, which generate diverse effects including photochemical, photo-thermal, photomechanical, or photo-electrical stimulation [5].

Interestingly, in the use of RL-TLCT, no standard protocol has been established in the literature; moreover, a few reports have shown studies using diverse parameters as varied wavelength ranges, time (sec/min), irradiance, or power density, and energy density with similar results, and important benefits in the brain health [5]. For example, studies applying Transcranial LED therapy bilaterally with wavelengths of 633 and 870 nm, have shown significant progress in both animals models with acute traumatic brain injury, and patients with acute stroke. In both cases also have been observed an improvement in the cognitive capacity post-treatment with this therapy [20]. Other studies using Low-level Laser Therapy (LLLT), with parameters of energy of 3 J/cm2 , a wavelength of 810 nm, and power density of 20 mW/ cm<sup>2</sup> , in primary cultured cortical neurons exposed to oxidative stress reveal that LLLT increased the mitochondrial membrane potential and reduced high ROS levels, reducing neuronal death [32]. Similarly, other studies showed that LLLT has a positive impact on neuronal function in both *in vitro* and *in vivo,* enhancing the metabolic capacity of neurons and cognitive functions including memory [14].

*Transcranial Red LED Therapy: A Promising Non-Invasive Treatment to Prevent Age-Related… DOI: http://dx.doi.org/10.5772/intechopen.100620*

Thus, while the transcranial research using RL LED or laser remains in the initial stages, growing evidence showed that although the RL and NIR-light therapy presents a wide range of characters, can modulate cell activity, including energy metabolism and cell function [25]. This is relevant since these therapies can lead to the improvement of pathological conditions and be in future significant clinical contribution, for example performing clinical treatments that allow helping older persons to prevent or mitigate the age-related cognitive impairment (**Figure 1**).
