Optical transmission measuring device and method of measurement

A method of determining optical transmission, T, of an object positioned in a measuring area exposed to incident light radiation, the method comprising:

• providing a measuring device comprising two sensors placed on a body, the two sensors being situated in a measurement plane and having the same spectral and directional response,
• arranging the measuring device at a first position relative to the measuring area so that both sensors are exposed to light of equal intensity,
• receiving first and second sensor outputs that are characteristic of a light intensity measured at each of the two sensors,
• moving the measuring device to a second position relative to the measuring area so that a first of the two sensors receives light transmitted through the object and a second of the two sensors receives unobstructed light,
• receiving a third output that is characteristic of a light intensity transmitted through the object and measured by the first sensor, and a fourth output that is characteristic of a light intensity measured by the second sensor,
• determining the optical transmission, T, of the object by evaluating the sensor outputs.

A measuring device for measuring optical transmission, T, through an object positioned in a measuring area between an external light source and the measuring device, the measuring device comprising:

• i. a body, two matched sensors placed on the body and being situated in a measurement plane;
• and
• ii. a control unit, operatively connected to the sensors to receive respective sensor outputs;
• wherein the body is configured to be moved between a first position in which a perpendicular projection of the measuring area onto the body does not overlap with either of the sensors, and a second position in which the projection of the measuring area overlaps with one sensor but not with the other sensor and the control unit is adapted to calculate a value T of the optical transmission of the object based on changes in the ratio of the sensor outputs of the sensors using the equation T=R/Rref, R=O21/O22, where O21 and O22 are the third and fourth outputs being characteristic of a light intensity measured at each of the two sensors in the second position, and Rref=O11/O12, where O11 and O12 are the first and second outputs being characteristic of a light intensity measured at each of the two sensors in the first position.