There are three major classes of color measuring instruments used in the textile industry: colourimeters, 0/45° and 45/0° geometry spectrophotometers, and integrating sphere geometry spectrophotometers. Colourimeters were early pioneers but have limitations as they cannot separate pure color from appearance or detect color changes under different light sources. Reflectance spectrophotometers measure the amount of light reflected at different wavelengths to produce a reflectance spectrum, which can be used to calculate CIE XYZ values. They illuminate samples with white light and calculate reflected light levels at 31 wavelength intervals using a monochromating device. Main components are a light source, optical system, light dispersing system, detector, and
2. There are three major classes of measuring
instruments available to the colouring of textile
industry. They are:
• Colourimeters
• 0/45° and 45/0° geometry spectrophotometers
• Integrating sphere geometry spectrophotometers
3. Colourimeters
• colourimeters were the pioneers of colour measuring
instruments. colourimeters view a sample through at least
three filters measuring the quantity of light reflected from the
sample and passed through each of the filters. The filters
were originally designed to mimic the response of the red,
blue and green cones of the eye as closely as possible. This,
at first glance, would seem to have merit since it attempted to
imitate the eye of the standard observer. An important
deficiency of colourimeters is they cannot separate the pure
colour from the appearance of an object. Additionally, a
colourimeter is unable to detect if an object’s colour will
appear differently under different light sources. Therefore,
colourimeters have limited capability when compared with
current technology.
5. Reflectance Spectrophotometer
• Reflectance spectrophotometers measure the
amount of light reflected by a surface as a function
of wavelength to produce a reflectance spectrum.
The reflectance spectrum of a sample can be used,
in conjunction with the CIE standard observer
function and the relative spectral energy
distribution of an illuminant, to calculate the CIE
XYZ tristimulus values for that sample under that
illuminant.
6. The operation of a
spectrophotometer is basically
to illuminate the sample with
white light and to calculate the
amount of light that is reflected
by the sample at each
wavelength interval. Typically
data are measured for 31
wavelength intervals centred at
400nm, 410nm, 420nm, ...,
700nm. This is done by passing
the reflected light though a
monochromating device that
splits the light up into separate
wavelength intervals. The
instrument is calibrated using a
white tile whose reflectance at
each wavelength is known
compared to a perfect diffuse
reflecting surface.
The reflectance of a sample is
expressed between 0 and 1 (as a
fraction) or between 0 and 100
(as a %). It is important to
realize that the reflectance
values obtained are relative
values and, for non-fluorescent
samples, are independent of the
quality and quantity of the light
used to illuminate the sample.
7. Reflectance Spectrophotometer
• Main component of a spectrophotometer are:
– Source of optical radiation
– An optical system defining the geometric conditions for measurement
– Light dispersing system
– Detector
– Signal processing system that converts light inti signals suitable for
analysis
