Spectroscope - Direct Vision.  The IEC spectroscope is a self contained device for separating the optical light components from a light source and for measuring their wavelength in nanometres. The instrument is hand held and is directed to the source of the light. The viewing hole carries a diffraction grating which behaves as a prism and causes the light source to deflect on its way to the viewer’s eye. Shorter wavelengths (higher frequencies) deflect more than the longer wavelengths. This deflection of the light rays makes the light appear to the viewer’s eye to be coming from inside the housing slightly to the viewer’s right hand side. A scale is mounted inside the box and this allows the amount of deflection to be measured and this deflection is calibrated as wavelength in nanometres. The various different components of colour that make up the original light source are easily seen as colour bands at various wavelengths.