. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. LIGHT SOURCES AND DETECTORS allowing a white surface to be lit by it, in turn measuring the luminance of the white surface. If a perfectly white screen which reflects 100 per cent of the light falling on it evenly in all directions is placed 1 m from a source of 1 cd it will have a luminance of 1 millilambert (mL) or 0-0003183 stilbs or 0-929 foot-lamberts () (see Table 1 for other units). Freshly deposited mag- nesium oxide has a reflecting factor of about 98 per cent. Radiation from
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. LIGHT SOURCES AND DETECTORS allowing a white surface to be lit by it, in turn measuring the luminance of the white surface. If a perfectly white screen which reflects 100 per cent of the light falling on it evenly in all directions is placed 1 m from a source of 1 cd it will have a luminance of 1 millilambert (mL) or 0-0003183 stilbs or 0-929 foot-lamberts () (see Table 1 for other units). Freshly deposited mag- nesium oxide has a reflecting factor of about 98 per cent. Radiation from incandescent solids A black body or full radiator might be defined as a body which absorbs light of all frequencies and reflects none of the radiation which falls upon it. The amount of energy radiated by a perfect full radiator varies as the fourth power of its absolute temperature. If the temperature of the full radiator is known, the spectral distribution of its radiant energy can be calculated by Planck's equation. The spectral distribution of energy at various tempera- tures is shown in Figure The radiation from a hot body becomes E o LlJ. * 2 3 15 ly'sl 20 A 6 810 X- I eohoo I 40 eo 200 103& Figure The spectral distribution of radiant energy emitted by an ideal black body at various absolute temperatures (after Sommer^). The shaded area represents the spectral limits of detection of the eye visible to the human eye at about 1,000°K, where 1 part in 10^ of the radiated energy is emitted in the visual range. A perfect full radiator does not exist in nature, although in some instances the energy distribution from a source approximates closely to a full radiator in the visible region. For example, the energy distribution of tungsten in the visible region approximates closely to that of an ideal full radiator at a 337. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration an
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