Radiometric and spectral characterization of multipanel planar light-emitting devices: a generalizable irradiance mapping approach for dose estimation.

Abstract

Significance: Accurate spectral and radiometric characterization of photobiomodulation (PBM) devices is essential for reliable dosimetry and reproducible therapeutic outcomes. Complex, multilight-emitting diode (LED) systems produce heterogeneous irradiance patterns that complicate dose estimation, underscoring the need for standardized quantitative methods.

Aim: To develop and validate a generalizable methodology for the spectral and radiometric characterization of multipanel and multi-LED PBM devices, demonstrated using the ATP38® system.

Approach: Spectral properties were measured using an optical fiber-based spectrometer. The radiometric properties were determined by measuring 2D irradiance maps acquired at a 4-cm working distance from a single panel at six wavelengths. A critical element of the method was correcting raw irradiance data for the detector's nonideal angular response, modeled by a ${\cos }^m\left(\theta \right)$ function, with $m$ determined for each wavelength. The corrected maps were fitted using double 2D Gaussian surfaces, enabling the generation of continuous irradiance distributions and their extrapolation to other working distances through homothety. This framework also allowed simulation of irradiance maps for multipanel configurations. To validate the physical characterization, in vitro experiments on normal human epidermal keratinocytes compared the biological effects of three illumination protocols applied at two panel locations. PBM effects were assessed by measuring the endogenously produced protoporphyrin IX fluorescence intensity and by the scratch test assay.

Results: Six emission peaks were identified at 454, 525, 594, 627, 729, and 842 nm. The detector angular correction improved the accuracy of the radiometric characterization, and Gaussian modeling of the irradiance enabled its prediction at different working distances. Biological responses correlated with spatial irradiance variations.

Conclusions: This framework enables quantitative characterization of the ATP38® device spectral and radiometric properties, supporting accurate light propagation modeling and dosimetry optimization.