Traditional light meters or photometers for Illumi­nan­ce measurement in lx (lux meter), lumi­nous flux in lm, luminance in cd/m² and luminous intensity in cd are built with an integral detector. The spectral sensi­tivity of the detector should match the spectral sensitivity of the human eye V(λ), as stan­dard­ized  by CIE and DIN.         

The adaptation of the photo­diode detector to the spectral V(λ) response is accomplished using a photometric correc­tion filter.

For radiometric light mea­su­re­ment such as Irradiance W/m², Radiant Po­wer W, Radiance W/(m²sr) and Radiant Intensity  W/sr, integral de­­tec­tors with a wavelength indepen­dent spectral sensi­tivity with­in a given spectral range,  VISIBLE, UV-A, NIR for example,  are in use.

For decades this type of light meter has been and still is the basic tool for all kind of light mea­sure­ment application in research and industry during the last time decades.

But today lighting and display in­dus­­tries continue to be trans­­­form­ed by new ge­ne­rations of light source techno­lo­gies.

Tra­di­tional incandescent lamps are being re­placed by discharge lamps, physical (LED) and organic (OLED) Light Emit­ting Diodes.  The CRT display makes way for LCD and Plas­ma Flat Panel Displays. 

These sources are characte­ri­zed predominantly by narrow wave­length band emission spectra.
Since the ideal integral detector with a perfect spectral match to the target standard spectral function does not exist, measurement uncertainty runs high or is often unknown when measuring test sources with a different spectral distribution than the calibration source, typically Illuminant A.

New alternative light meter techno­logies are required that can offer precise and trace­able light measure­ments in abso­lute units. The measurement uncertainty of the readings should be independent of the light source emission spectrum.
The X4 light analyzer from Gigahertz-Optik offers a uni­que Bi-Tech Sensor Tech­no­logy that combi­nes an integral sensor with a diode array spectro­me­ter to form a cost effective and accurate light meter which benefits from the advan­tages of both techno­logies and compen­sates for their limitations.

Universal accessories for light measurement and light source control test set-ups  supporting the X4 as well as traceable calibration services are described in full detail on the next pages.