Reflectance Spectroscopy
Definition
Measurement of the proportion of incident light reflected from a surface at each wavelength. Absorbing chromophores (such as haemoglobin) reduce reflectance at their characteristic wavelengths, producing absorption features in the spectrum.
- Measures
- Proportion of incident light reflected at each wavelength
- Application
- Bloodstain age estimation via haemoglobin absorption features
- Mechanism
- Chromophore absorption reduces reflectance at characteristic wavelengths
Common questions
Why does haemoglobin's reflectance signature change as a bloodstain ages?+
Haemoglobin oxidises over time through oxyhaemoglobin, methaemoglobin, and further degradation products, each with a different absorption profile, so tracking how the reflectance spectrum shifts gives a way to estimate how long the stain has been present rather than just confirming blood is present.
What environmental factors can confound a reflectance-based bloodstain age estimate?+
Substrate colour, humidity, temperature history, and UV exposure all influence the oxidation rate and the surface's own reflectance, so a calibration built under one set of conditions will not transfer reliably to a stain that aged under very different conditions.
Related terms
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- Validation
- The process of establishing through systematic testing that a method does what it claims to do, within defined conditions and with a...