Universal Reflectance Measurements

The ReflectaScan Reflectance Spectrophotometer is designed as a universal reflectance measuring instrument capable of scanning samples over the wavelength range 190-1000nm. An integral printer plots results and an external dot matrix or colour inkjet printer may be used if required.

Diffuse Reflectance Measurements

The integrating sphere system allows a range of measurements to be made.

• Diffuse and specular samples
• Total hemispherical reflectance
• Specular excluded diffuse reflectance
• Transmittance of turbid or scattering samples
• Diffuse reflectance of powder samples

The compact sphere, which mounts within the instrument's sample compartment, is made from Spectralon^TM which has the highest reflectance over the UV and visible region of any known substance. This gives high energy throughput resulting in excellent performance. The design is versatile, easy to use and allows for the elimination of substitution errors.

A 0° sample rest enables measurements to be carried out with the specular component eliminated. Substituted by a 11° sample rest, total hemispherical reflectance is measured.

Diffuse Reflectance

A dedicated high performance Spectralon^TM integrating sphere is used for diffuse reflectance and diffuse transmittance measurements. The sphere unit has its own silicon diode detector which uses a separate signal channel within the Spectrophotometer.

Turbid or Scattering Samples

The sphere unit is equipped with a 10mm pathlength cuvette holder so that transmittance measurements may be made for both turbid or normal samples. Scattering films may also be accommodated for measurement.

Specular Reflectance

A dedicated specular reflectance unit is used for specular reflectance measurements of surfaces and coated opthalmic lenses. The unit is ideal for quality assurance in the production of anti-reflection coated opthalmic lenses, many of these systems are now in use around the world.

Diffuse Reflectance of Samples

All scans were made with the specular component excluded.

Coated Lens Reflectance

The optical performance of the anti-reflection coatings on opthalmic lenses is specifically catered for by the specular reflectance unit. A conical rest is provided to accommodate lenses up to 80mm diameter. Measurements are made with reference to an uncoated lens and the system is excellent for the production control of vacuum coated lenses. Many of these systems are now in everyday use.

Opthalmic Lens Transmission

The transmission characteristics of tinted opthalmic lenses may readily be measured using the CE 3077 lens mounting system. This allows the lens to be accurately centred on a carrier plate which is kinematically mounted on the body of the lens holder.

Measurement of Thin Films

Using the CE 3075 specular reflectance unit, the thickness of films deposited on a surface, for instance a epitaxial film of silicon dioxide on a silicon wafer, is readily measured.

The reflectance scan of such a film against wavelength produces a series of transmission maxima and minima due to the interference between energy reflected from the front surface of the film and that reflected from the interface between the film and its substrate.

Film thickness is calculated from an equation relating the number of peaks to their wavelength separation. Films down to about 0.1 microns in thickness may be measured.

A scan of a deposited film is shown here, the film thickness was calculated to be 1.05 microns.

Colour Computations

Software is available (colour) to enable a wide range of calculations including tristimulus values, chromaticity, CIE L* A* B, CIE L* U* V, Hunter, metric colour, whiteness and yellowness.

Standard illuminant tables include CIE, A, B & C and CIE D50, D65 & D75. Observer tables include 2° and 10° angles.

Shown here is part of a complete printout from a light blue paint sample produced by the colourz software programme.