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OL0028 - Ambient Light Analyzer

The Ambient Light Analyzer OL0028 has been developed for measuring the illuminance in the unit Lux [lx] and the color of the incident light. The meter can be used as a handheld unit but also provides a mounting option useful, for example, when performing stationary long-term measurements.

A standard USB connection is used for both voltage supply and communication. For this purpose, the instrument logs in to the operating system as a USB HID device. Since this device class is already included in all current operating systems, no additional drivers have to be installed! This also makes it relatively easy to integrate the measuring instrument into application-specific software. For this purpose, comprehensive documentation of the command set is available.

For assessing the accuracy of illuminance measuring instruments, especially of filter-based meters, many suppliers refer to the adjustment of the actual filter function to the V(λ) function as, for example, defined in and required by the DIN 5032 or EN 13032 standards. Errors in the real filter function result in measuring errors. Fatally, though, the gravity of these errors differs from one type of light source to another! In principle, this would allow, for example, to very precisely measure a red LED whilst using the same filter for measurement on a blue LED would produce a very substantial measuring error.

The way the DIN 5032 standard rates the ‘quality’ of different classes (key word: ‘f1’ index“) does not allow to make any reliable general statement about the measuring accuracy to be expected. This applies in particular when the light sources to be measured are LED-based or otherwise contain high proportions of energy in ‘narrow-band peaks’.

Realizing the corresponding filters in practical application in a physically precise and thus ‘V(λ) compliant’ way is a very complex task, partly resulting in considerable differences between the illuminance meters available in the market. As described above, it is easily possible that a calibrated meter identified as ‘Class B’ with a very high accuracy level can produce significantly poorer results than a calibrated ‘Class C’ meter.

Many measuring instruments allow the use of light-source specific correction factors. Whilst this is certainly helpful, it often makes it difficult for the end user to select the suitable factor. This poses significant problems, especially with modern LED-based light sources.

The Ambient Light Analyzer OL0028 not only has the capacity to measure the illuminance but also the color of the incident light. For this purpose the instrument uses an XYZ sensor in accordance with the CIE1931 standard integrated into the front end. The Y channel in particular provides the required V(λ) function. Taking only the Y channel into account, the result is a ‘Class C’ meter.

The supplied factory calibration for the OL0028 is performed on the basis of a NIST-traceable calibration lamp corresponding to a broadband emitter. This calibration is valid for the unchanged real V(λ) function of the sensor used and thus fulfills the same requirements as current ‘Class C’ luxmeters. Additionally, we have developed a process used for generating an additional factory calibration valid for all black bodies within a range of 2000K to 10000K which is also checked and documented for the NIST lamp. Both factory calibrations are certified by us accordingly.

In addition to these two calibrations, the user can select between 253 further calibration sets, enabling precise adjustment not only of the measured illuminance but also of the color values based on established matrix calibrations. The major difference to the correction factors usually used for luxmeters is that the user calibration also influences the spectrum of the filter functions, thus enabling a more precise and more tolerant correction.

And, as the name implies, the calibration can be performed by the user himself, provided that suitable references are available to him.

To support this, we provide the corresponding tools and are able to perform and document a customer-specific factory calibration for you to ensure that your measuring results are optimally tailored to the characteristics of your specific application.

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Technical data

Power supplyUSB 5V
Power input35mA
Connection
  • Exchangeable USB 2.0 cable, USB Micro-B port, screwed strain relief provided on the instrument
  • Digital IO, 3x socket contacts with 2.54mm pitch spacing. Suitable for the connection of precision connectors
Wavelength rangeVIS, 380nm – 780nm
Measured variable
  • Illuminance in [lx]
  • CIE XYZ (CIE1931 2° Standard Observer)
  • Chromaticity xy, color temperature CCT, dominant wavelength Ldom (calculated)
Optics
  • Fixed lens with diffusor for cosine correction
  • Highly sensitive XYZ sensor on the basis of long-term stable glass interference filters
Measuring method and parameters
  • Integrated A/D converter for direct measurement of photocurrents
  • XYZ sensor in the front end
  • Integration time from 1ms to 1024ms in 11 increments
  • Analog gain in 5 increments
  • Averaging over 1 to 1024 measurements
Calibration of the measuring instrument
  • Standard factory calibration to NIST-traceable spectral-irradiance standard (200W quartz halogen lamp)
  • Based on spectral data of a reference light source and precisely measured, individual filter functions of the measuring instrument, a new user calibration for new types of light sources can be performed without taking real measurements (OPTO4L VirtuCal)
  • Separate calibration for color and intensity
Number of possible user calibrations
  • 256 user calibrations can be retentively stored in the instrument
  • Adjustable to new types of light sources by the user at any time
Digital IO
  • 1 output, 3.3V/40mA
  • 1 input, pull-down contact, Iin<1mA
Communication
  • Text readable command set, for direct application by the user using the terminal functions of suitable tools
  • USB HID class, no drivers required from WIN7, iOS and Android
  • Pure master/slave communication in 64byte blocks, 4ms cycle time
  • Firmware update is possible at any time
Measuring rangeIlluminance <0.1 Lux to >100000 Lux
Accuracy
(following light-source specific extended calibration)
  • Illuminance ±3% within a range of 1 Lux to 100000 Lux
  • Chromaticity ±0.0025 at approx. 3000K, ±0.007 for monochrome colors
  • Repeatability ±0.00005
CasingPA12 plastic, painted black
Weight (without cable)35 g
Temperature range10°C to 60°C
(internal compensation within a range of 10°C to 55°C)