Light sources

There are many low cost artificial light sources used for illumination or for industrial applications: tungsten or halogen bulbs, fluorescent lamps, LED lamps etc. Some of these sources offer regulated intensity of emitted light. However, there are very few calibrated light sources of precisely known photometric/radiometric parameters. A light source can be considered as calibrated when its user can precisely regulate its photometric/radio­metric parameters like luminance (or illuminance), radiance (or irradiance) at defined spectrum of interest.  Such light sources are needed in many applications including  systems for testing night vision devices, VIS-NIR  cameras and SWIR imagers.  Another critical requirement on professional calibrated light sources is ability to simulate illumination conditions met at real life conditions. Practically it means ultra high dynamic of regulation of light intensity to simulate both day/night conditions and to simulate different light spectrum.  Inframet offers a series of calibrated light sources that can be divides into three groups:

    1. Multi-channel halogen/LED light sources,
   2. Single channel halogen light sources,
   3. Large emitter light sources.

The light sources from the first group  (coded as DAL/SAL light sources) are optimized to be used in systems  for testing VIS-NIR cameras and SWIR cameras. These sources are expected to simulate illuminance conditions met in real life scenarios: from dark nights in Afghanistan mountains to ultra bright days in Arabian deserts. Such realistic simulation is possible only using light sources of following features:

  1. Ultra high dynamic (ratio of maximal light intensity  to minimal  light intensity) of light source at level over 10^10 (needed to simulate both bright days  and dark nights),
  2. Variable light spectrum in VIS-SWIR range (needed to simulate variation of spectrum of incoming light and variation of reflecting properties of targets under surveillance),
  3. Ability to emit high intensity UV light (needed to simulate conditions met at coastal areas or high altitude mountains with high UV light that are potentially damaging for some imaging sensors).

Two light sources codes as DAL/SAL belong to the first group. These light sources work by com­bining light from several channels: halogen bulb of 2856K color temperature spectrum and several LED sources. Intensity of the halogen bulb is regu­lated using an opto-mechanical attenuator that changes light intensity but does not change light color temperature. Intensity of the LED sources is regulated electronically using advanced electronic regulation/stabilization system. Intensity of UV LED is not regulated. Spectrum of emitted light can be regulated by switching light channels or by mix­ing light from halogen channel with LED channels. Regulation of spectrum of emitted light is addition­ally supported by a set of external spectral filters. DAL/SAL light sources look externally the same but there are some design differences: different coating of integrating sphere, slightly different halogen source and different LED sources. DAL is optimized for testing VIS-NIR  cameras sensitive up to about  1000 nm; SAL – for testing SWIR im­agers sensitive up to about 1700 nm.  DAL source is used a crucial block in TVT systems for testing VIS-NIR cameas, SAL source as a crucial block in ST system for testing SWIR imagers.

Fig. 1. Photo of DAL  light source

Fig. 2. Photo of SAL  light source


H40 is a single channel source halogen light source that emit light of 2856K spectrum. Technically it can be treated as a simplified DAL light source without LED channels and with modified light emitter. Diameter of light emitter in H40 sources is the same as in DAL/Sal sources (40 mm) but there are two important changes: a) Lambertian source at emission at angles up to 60°, b)ability to cooperate with bright collimators of low F-number (ratio of focal length to aperture can be as low as one).

The second change means that by using additional bright collimator an apparent aperture of the light source can be increased (typically up to 200mm) while still keeping sufficient emission angle. Practi­cally it means that H40 light source cooperating with a series of bright CRAD refractive collimators makes possible calibration of VIS-NIR cameras or SWIR cameras with optics as big as 200mm.

Fig. 3. Photo of H40 light source

Fig. 4. Photo of H40 light source integrated with CRAD collimator

Ability to calibrate VIS-NIR cameras and SWIR cameras of big optics can be also directly obtained by using light sources of big emitter. Two such light sources are offered: L150 and H150.  L150 is a single channel, ultra compact (thin de­sign) LED source that emits light using emitter of 150mm diameter. Emission in different spectral bands is possible: visible, NIR or in SWIR.   H150 a single channel, halogen source that emits light using emitter of 150mm diameter. The source emits polychromatic light of 2856K spectrum in VIS-SWIR range.

Fig. 5. Photo of L150 light source

Fig. 6. Photo of H150 light source