Evaluating onions quality using optical techniques is challenging because the presence of outer dry skin and
the layered structure of onion fleshy tissues. To better understand the light propagation in onions, the optical
properties of dry skin and fleshy tissues from two cultivars were measured at 632.8 nm by using a single integrating
sphere based system. Onion tissues were cut into 30 mm square pieces and sandwiched by Borofloat glass slides.
The total diffuse reflectance, the total transmittance, and the collimated transmittance of the onion samples
were measured by an integrating sphere system with a VIS-NIR spectrometer. The absorption coefficient (μ<sub>a</sub>),
the reduced scattering coefficient (μ<sub>s</sub>'), and the anisotropy coefficient (g) of onion tissue samples were estimated
using the inverse adding-doubling method based on the measured spectra. The light propagation in onion tissues
were modeled based on the calculated optical parameters using Monte Carlo simulations. The results indicated
that onion tissues are high albedo biological media. Onion dry skins have much higher absorption and reduced
scattering coefficients than onion fleshy tissues. Comparisons between the two onion cultivars showed that the
optical properties of onions could vary with cultivars. The results of this study can be used to develop appropriate
optical approaches for the onion quality inspection.