Color Instruments Metrology

• Repeatability
Repeatability is how well an instrument can repeat identical measurements.
Repeatability can be quantified in terms of short, medium, and long times between
measurements. These types of repeatability are taken over seconds or minutes (short); hours (medium); and days, weeks, or longer (long). Intuitively, repeatability can be thought of as the degree to which an instrument makes self-consistent measurements.

• Reproducibility
Reproducibility is similar to repeatability except that some aspect of the
measurement conditions have changed. This might be the operator, the instrument, or some
other condition. The intuitive understanding of reproducibility is the degree to which an
instrument makes consistent measurements even when conditions are slightly changed.

• Inter-instrument and Inter-model Reproducibility
These are special cases of repeatability where instruments of identical design (inter-instrument) or different design (inter-model) are compared.

• Accuracy
Accuracy is how closely an instrument can conform to the accepted value for a given sample. “Accepted” values are usually provided by a high-accuracy laboratory, such as a national standards body. From these samples, accuracy is independently determined for the wavelength scale and the radiometric scale.

http://www.color.org/ICC_white_paper_22_Precision_and_Bias_in_Measurement.pdf

Radiometry and Photometry

Lighting terms can be rather technical and confusing. This may help.

Radiometry is the science of the measurement of electromagnetic (EM) radiation. The broader spectrum covered by the science of radiometry is based on physical constants.

The properties of concern to us here are radiated power and its spatial and angular distributions. The four basic concepts are:

1. Radiant Flux
2. Radiant Intensity
3. Radiance
4. Irradiance

Photometry is defined as the measurement of electromagnetic energy that is visible to the human eye.

In 1942 the Commission Internationale de l’Eclairage (CIE) convened to define the response of the average human eye. They defined the Standard Luminosity Function also known as the Photopic curve and the Scotopic curve.

Photometric quantities are derived from radiometric quantities by utilizing a filter which approximates the behavior of the average human eye as defined by the CIE.

A radiometer is a device that measures the intensity of radiant energy. A majority of radiometers utilize only a single sensor whether photocell, photo-multiplier tube (PMT), etc. An optical filter is normally used when measuring radiation emitted from a specific spectrum or to incorporate the radiometer within a certain spectral response.

Radiometers are commonly used to quantify light or energy outside the visible spectrum, i.e., ultraviolet and infrared. Depending on the specific application, different filters with specific spectral responses are used.

A photometer is defined as an instrument for the measurement of visible light. The most common types are the luminance and illuminance meters.

The basic difference between photometers and radiometers is that the photometer incorporates a filter which follows the CIE Standard Luminosity Function Vλ curve (shown below).

Konica Minolta Sensing Inc published a booklet - The Language of Light which helps make the complicated lighting terminology simple for applicators.

Write to me if you need a copy.