PATIENT FACING SYSTEMS Measurement of Physical Parameters and Development of a Light Emitting Diodes Device for Therapeutic Use Rinaldo Roberto de Jesus Guirro 1,2 & Gabriela de Carvalho 1,2 & Aline Gobbi 1,2 & Flávia Fernanda de Oliveira Assunção 1,2 & Nathalia Cristina de Souza Borges 1,2 & Luciano Bachmann 3 Received: 25 November 2019 /Accepted: 2 March 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Introduction: Effectiveness of light-emitting diode (LED) in biological tissue is due to the correct application of physical parameters. However, most studies found do not provide complete information on the physical characteristics of the diodes. It is necessary to carefully evaluate the diode parameters so that the results of research with this feature can be reproduced. The objective of this study was to develop a light-emitting device using LED, with proper measurements for application in clinical research. It was used 267 LEDs, powered with 12-V voltage and fixed on a plate of ethylene-vinyl acetate (25× 42 cm), equidistant at 1.0 cm. For the calculation of red and infrared irradiation, a spectrometer was used, and the data were processed in routines implemented in the OriginPro 8.5.0 SR1 Software. The irradiance was determined by the integration of the spectral irradiation in the LED emission region. The red LED has a wavelength of 620 ± 10 nm, a power density of 52.86 mW/cm 2 , power of 6.6 mW, and total power of 1.76 W on the device. The infrared LED has a wavelength of 940±10 nm, power density 33.7 mW/cm 2 , power of 6 mW, and total power of 1.6 W on the device. The LED characterization enables the generation and application of energy with greater precision and reproducibility. Besides, it is a light source, a device capable of framing large areas, reducing the time and cost of the application in different clinical conditions related to neuromuscular performance or rehabilitation. Keywords Light-emitting diodes . Low-level light therapy . Devices . Radiation Introduction Light Emission Diode (LED) phototherapy has recently intro- duced in the area of physiotherapy with promising results. This light source differs from low-intensity laser therapy in that it has a greater beam divergence and higher spectral band- width [1]. The effectiveness of the LED in biological tissue is due to the correct application of physical parameters, which must be clearly known and adequately verified. The main parameters being wavelength, power, and irradiance (power density). Therefore, the quantitative verification of LEDs with specific equipment for checking, valid, and reliable photobiophysical measurements is essential, especially for health studies [2]. Health studies are conducted with this resource in recent years. It has frequently used with promising results in bacteria inactivation [3–6], aerobic training performance [7, 8], and tissue healing [9–12]. It is worth noting that LED therapy is a viable phototherapy modality due to its low cost and easy application [13]. However, most studies involving LED do not provide ad- equate information about the physical characteristics of the diodes, as well as the measurement of the optical characteris- tics of the light and the power supply. This leaves a gap in the reliability of the results, considering that the biological This article is part of the Topical Collection on Patient Facing Systems * Rinaldo Roberto de Jesus Guirro rguirro@fmrp.usp.br 1 Laboratory of Physiotherapeutic Resources, Postgraduate Program in Rehabilitation and Functional Performance, Department of Health Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil 2 Department of Health Sciences, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil 3 Ribeirão Preto School of Philosophy Sciences and Letters, University of São Paulo, Ribeirão Preto, SP, Brazil Journal of Medical Systems (2020) 44:88 https://doi.org/10.1007/s10916-020-01557-y