Plastic bottles are diverse in size, shape and colour. As is common to all plastic products, bottles can be opaque, translucent or transparent. The requirements for colour measurement can extend past transmitted or reflected spectral data to also include CIE L*a*b* Colour, Yellowness, Haze and other appearance related attributes. Plastic sample type will dictate the proper measurement instrument and technique according to the HunterLab guidelines set forth below.

Opaque Bottles are impenetrable by light, and are best measured using a Directional 45°/0° reflectance instrument, or Diffuse d/8° Sphere reflectance instrument:

  • If you are measuring opaque bottles and desire to quantify a numeric value to visual perception, then the proper measurement technique is to employ a reflectance spectrophotometer that uses Directional 45/0° reflectance geometry. This is the geometry that most closely matches how the human eye sees colour.
  • If you are measuring opaque bottles and desire to negate the gloss and texture component of the sample and look at colour only, then the proper technique is to employ a Diffuse d/8° reflectance instrument.

Translucent Bottles allow light to pass through, but only diffusely, so that objects on the other side cannot be clearly distinguished. Both reflective and transmittance measurement modes may work well depending on the translucency of the sample.  As a rule of thumb,

  • If at the path length that your customer will view the sample, you can see slight details of your thumb or finger through the plastic, then transmittance is the preferred measurement method.
  • If you cannot see slight details, then reflectance is preferred.

Path length is defined as the thickness of the sample from where the light enters to where it exits the sample.

Transparent Bottles allow light to pass through with little or no interruption or distortion so that objects on the other side can be clearly seen. These bottles can only be measured using transmission instrumentation.

Additionally, certain metrics and indices such as CIE L*a*b* Colour, Whiteness, Yellowness and Haze require the use of specific geometries and specific measurement modes.

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