ntegrating sphere technique is widely used to
measure the total reflectance and transmittance of turbid
sample, but the unavoidable light loss induces some
measuring error. It has never been reported whether the
error depends on the shape and size of light beam. In this
paper, a convolution for computing the responses to
rectangular incident light beam based on the Monte Carlo
method was presented. The effects of light beam shape and
size, and optical properties of sample on the measurements
were addressed. The results show that the light loss with
rectangular incident light beam is larger than that with
circular one with the same area. The more the area of light
beam, the more the light loss. And the light loss induced by
the optical properties of sample is much more significant
than that by the shape and size of the incident light beam.

• Integrating sphere technique is widely used to measure the total reflectance and transmittance of turbid sample, but the unavoidable light loss induces some measuring error. It has never been reported whether the error depends on the shape and size of ligh