We propose a new parameter obtained by three-fiber-based diffuse reflectance spectroscopy for nondestructive measurement, demonstrating a good linear correlativity of the parameter with the fruit sugar content by employing LEDs as light sources.Sugar content, one of the most important attributes in determining the quality of fruit including apples, is normally measured using destructive juice-extraction methods, such as Brix refractometry. Several nondestructive near-infrared spectroscopy methods determine fruit sugar content using a spectrometer [1].We proposed a three-fiber-based diffuse reflectance spectroscopy (TFDRS) method [2], which enables us to measure fruit sugar content nondestructively using near-infrared lasers. The geometry of TFDRS is shown in Fig. 1. A sample is irradiated with a laser through an emitter fiber, and the diffusively reflected light from the fruit is detected by two receiving fibers positioned at distances of U and U +' from the emitter fiber. Reflectancewhere P k (U) and P k (U ') are the diffuse light powers reaching the receiving fibers at U and U +', respectively.In addition, we have introduced a relative absorbance ratio J with respect to three wavelengthswhich is expressed as follows:where R 1 , R 2 , and R 3 are reflectances obtained by TFDRS at illumination wavelengths O 1 , O 2 , and O 3 , respectively. The value of J is independent of the optical path length determined by the reduced scattering coefficient of a sample and exhibits a good linear correlativity with the fruit sugar content C (Brix% or wt%): J = b 0 + b 1 x C. As a result, the value of J enables us to nondestructively measure fruit sugar content with a practical accuracy of 0.5 Brix% or less using lasers at three different wavelengths in the near-infrared region (900 -1070 nm) [3].In contrast, a variation of J by the reduced scattering coefficient P s ' of a sample increases with increasing spectral linewidth, resulting in insufficient correlation of J with sugar content C to achieve the practical accuracy of 0.5 Brix% or less at a spectral linewidth FWHM > 10 nm. Therefore, using a light emitting diode (LED) with a spectral linewidth of about 50 nm at FWHM as a light source of the TFDRS is not possible. However, commercial LEDs are less expensive than laser diodes, thus LEDs are very attractive as a light source for an inexpensive portable instrument, which is suitable for orchards.In this work, we propose a modified relative absorbance ratio *, which has a good linear correlativity with the fruit sugar content C at a spectral linewidth FWHM >10 nm, enables us to employ LEDs as a light source of the above TFDRS, and demonstrated a verification of the proposed value * by using commercial near-infrared LEDs. Fig. 1 Geometry of three-fiber-based diffuse reflectance spectroscopy (TFDRS).The theoretical results of each squared correlation coefficient R 2 that fits relationships of J = b 0 + b 1 x C and J = b 0 + b 1 x C + b 2 x P s ' are shown in Fig. 2. Here, J is determined at three wavelengths (O 1 , O 2 , O 3 )...