Lux Meter or Lumeter (Holophone Lumeter)

Lux Meter or Lumeter (Holophone Lumeter) Points : Lux Meter or Lumeter (Holophone Lumeter) The schematic arrangement of Lumeter or Lux meter. When the photometer is used the brightness of an internal white comparison surface, illuminated by light from a lamp inside the box, is adjusted, by rotating a disc having a sector-shaped opening, until it matches the brightness of the test surface. The light from the lamp, whose output is maintained at a fixed value by a resistor, is diffused by an opal glass window. Colour filters may be interposed between this window and the comparison surface to match illumination by yellow or blue-green light.

One scale of the instrument is marked to read the illumination of the test surface in lumens per square foot and another is graduated to read the luminance (brightness) of this surface in foot-lamberts. The range of illumination which can be covered is from 0.002 to 8000 lumens per square foot.