Luminance Irradiance DEF


LED and Solid state lighting [SSL] is often referred to as the light of the future: combining low energy consumption, efficient technology and long product life times. An inherent challenge to the production process of LEDs and Solid State Lighting products are driver related variations in their optical characteristics such as brightness, color and flicker, even in the same production batches. In order to assure a high-end lighting product, it is necessary to measure these optical characteristics during the development of LEDs and perform a 100% inspection during the production processes. Typical LED – SSL measurements include:

Geometry & optical configurations

Radiometric Spectroradiometric Photometric
Integrating sphere Radiant power [W] Spectral radiant power [W/nm] Luminous power [lm]
Cosine corrector* Irradiance [W/m²] Spectral irradiance [W/m²/nm] Illuminance [lm/m² = lux]
Cosine corrector* Radiant intensity [W/sr] Spectral radiant intensity [W/sr/nm] Luminous intensity [lm/sr = cd]
Lens Radiance [W/m²/sr] Spectral radiance [W/m²/sr/nm] Luminance [lm/m²/sr/ = cd/m² = nit]

*Instead of cosine correctors, integrating spheres can also be used to determine [spectral] irradiance and radiant intensity / illuminance and luminous intensity. Flicker measurements can be carried out in combination with any of the optical configurations mentioned in the table above.

  • Spectral power distribution to determine a light source’s total emitted power for each individual wavelength revealing information like for example color, CRI, CCT and many more.
  • Radiance, irradiance & radiant intensity measurements to measure the amount of radiant power in W/m²/sr, W/m² and W/sr and parameters such as PAR.
  • Luminance, illuminance & luminous intensity measurements to determine the light output in candela per square meter, lux and candela respectively.
  • Flicker measurements to determine and adjust for flickering of light sources. Currently supported: flicker %, index and IEEE 1789 recommendation.
  • 2D luminous surfaces measurements determine aspects such as uniformity of large luminous panels or surfaces.

How are you measuring?

With fibers and other accessories even more type of measurements are possible. Often used accessories are integrating spheres, cuvettes for fluids, light sources or filter holders.

Consumers are used to enjoy top-quality displays in their mobile phones, tablets, laptops and even cars. Emerging technologies such as lighting surfaces for office and home illumination are expected to look equally perfect. Both displays and luminous surfaces are the main application areas for imaging colorimeters.