Process and apparatus for determining the properties of a piece of timber

The invention relates to a process and an apparatus for determining the properties of a piece of timber in connection with the manufacture of wood products. According to the invention a wood sample is selected from the piece of timber; the wood sample is illuminated by a light source selected from a UV light source, visible light source and their combination; the resulting signals are observed and analyzed from the wood sample illuminated by UV light based on fluorescence differences and from the wood sample illuminated by visible light based on a color difference; and properties selected from the group of decay, rot fungus, blueness, dead or sound knot, cracks, bores, dirt, site of heartwood, amount of heartwood, location of pith, amount of sapwood, wane, location of the piece of timber on a log and their combinations are determined from the wood sample by the signals.