BPC300-C Photochromic Contact Lens Spectrophotometer

The BPC300-C is a complete solution for the automatic characterisation of photochromic (sun-darkening) prescription contact lenses. Multiple samples can be mounted in the temperature-controlled water bath housing an automatic lens carousel, and can be analysed sequentially and automatically, resulting in machine readable files and PDF reports of the measured characteristics. 

Spectral and time-resolved transmittance/optical density measurements can be performed at various temperatures in darkness and under the intense irradiation of a nominally AM2 (but highly configurable) conditioning beam, which allows darkening and fading-back kinetic studies

Full characterisation sequences including preconditioning, faded spectral optical density measurements, darkening dynamics measurements, darkened spectral optical density measurements, fading dynamics measurements, and spectral optical density measurements after fading can all be performed sequentially on up to 6 samples without requiring user interaction. 


The BPC300-C gives you control over the measurement process and environment, allowing you to develop your photochromic lens technology as required, from small-scale laboratory use to larger process-monitoring applications.

Control ambient conditions

  • AM2 conditioning source with the facility to attenuate and filter the spectrum to produce multiple software-selectable conditioning beams with different characteristics
  • Fully temperature controlled water bath allows measurements between 20°C and 50°C, ±0.2°C
  • Precondition your samples in a standards-compliant manner

Perform detailed measurements

  • Spectral optical density measurements between 280nm and 780nm in darkness or under activation light

  • The water bath and integrating sphere allow you to make measurements independent of sample optical power

  • Automatic conditioning beam illuminance intensity validation

Set multiple measurements going at once

  • 8 position sample carousel (6 samples, 1 clear aperture, 1 photodiode) allows the sequential measurement of up to 6 samples without user interaction.
  • Reference measurements are automatically performed before each measurement, with in-process monitoring to alert for issues occurring during the measurement. 

  • The system can provide files for your laboratory information management systems (LIMS) and output a PDF report for each of your samples.

Leverage existing standards

The calculations for many photochromic spectacle standards are also available for your contact lenses:

  • ISO/ EN 8980-3:2013 - "Ophthalmic optics. Uncut finished spectacle lenses. Transmittance specifications and test methods."
  • ISO/ EN 12312-1:2013 - "Eye and face protection. Sunglasses and related eyewear. Sunglasses for general use."
  • ANSI Z80.3: 2015 - "Non-prescription Sunglass and Fashion Eyewear Requirements."
  • AS/NZS 1067-2016 - "Sunglasses and fashion spectacles."

The system calculates parameters such as luminous transmittance in faded and darkened states, photochromic response, various lens categories, colourimetric parameters, visual attenuation coefficients for red, green, blue and yellow traffic lights, and many more.


More details of the components of the BPC300-C system are available on the Configuration page.

Measurement Specifications

Spectral range of operation 350-780nm, 280nm-780nm optional, contact us for other ranges
Bandwidth 5nm
Wavelength accuracy ± 0.15nm
Beam diameter at sample plane 5mm
Measured transmission range 0.5-100%
Conditioning beam AM2 with requirements of ISO8980-3:2013
Optional filtering
Temperature range 20-50°C
Temperature stability ± 0.2°C
Bench space required 1m deep x 1.5m wide for bench top assembly, see Dimensions for details
Services requirements 5 x main sockets 1200W power consumption
Dry gas supply where measurements below ambient are required

Monochromatic Probe Source

Probe source 250W Quartz Halogen lamp, Deuterium source optional for 280nm
Monochromator configuration Symmetric, single Czerny-Turner source, second matched monochromator for acquisition
Monochromator focal length 300mm
Diffraction gratings 1800 g/mm standard, additional options available
Diffraction grating mount Triple grating turret
Dispersion 4.05nm/mm
Bandwidth 5nm standard, additional options available
Wavelength accuracy ± 0.15nm standard
Chopping frequency 175 Hz (typical)
Beam diameter at sample plan 5mm diameter

Water Bath

Temperature range 20-50°C
Temperature stability ± 0.2°C
Temperature accuracy ±1°C
calibratable and supplied with calibrated thermometer and mount

Conditioning Beam

Spectral match AM2 with requirements of ISO8980-3:2013
Beam illuminance 0-50klx
Beam filtering Optional filtering
Number of configurable apertures 4
Number of configurable filters 6
Nominal AM2 conditioning beam, can be attenuated and filtered.

Computer Control

OS Windows 10, (typically works on Windows 7 but technical support capability is limited)
Software control BenWin+ Spectral acquisition software, PhotoBench utility
Minimum hard disk space Approx. 100MB
Minimum RAM 2 GB
Interface 4 x USB 2.0 ports

Components and Options

The BPC300-C is a complex system. This page outlines several of the key components and shows what standard options are available.

TMc300 Monochromator


The spectral transmittance measurements are based upon two Bentham symmetric Czerny-Turner monochromators. These precision devices achieve a wavelength accuracy of ±0.15nm using their 1800nm gratings, and are typically configured for a bandwidth of 5nm. Due to the measurement geometry, the calibration of these devices can be verified in-situ with an optional absorptive standard that can be mounted in the beam path for field-recalibration1.


  • Two single Symmetric Czerny-Turner monochromators moving in tandem:
    • monochromator 1 acts as a tunable light source, producing a monochromatic probe beam
    • monochromator 2 acts as a tunable filter, attenuating the conditioning beam but allowing the probe beam to pass
  • 300mm focal length
  • 5nm bandwidth (configurable with replacable slits)
  • ±0.15nm wavelength accuracy
  • up to three gratings per monochromator are possible. 


Notes: 1. The accuracy that can be achieved with field-recalibration with an absorptive standard may be lower than factory calibration.

The water bath's temperature control block seen from the rear of the system.

Water Bath

The unit houses a container with apertures for the probe and conditioning beams that allows the sample lenses to be placed in a water bath, both to supply a temperature-controllable medium as well as to reduce the effective optical power of the lenses being measured. An integrating sphere on the output catches light at whatever deviation remains.


  • Peltier heated and cooled, 20°C-50°C
  • Temperature sensor
  • PID temperature control to within ±0.2°C
  • Fill funnel, drain valve
  • The enclosure has a dry-gas purge capability to prevent fogging of the windows at or below ambient temperature
  • Continuous gentle mixing by an immersed impeller to prevent temperature gradients
BPC300-C Carousel with 6 sample holder (+ photodiode and clear aperture)


The carousel is a device placed into the water bath to hold and automatically change between 6 samples, a clear aperture, and a lux-measuring photodiode to monitor conditioning beam intensity between sample measurements.

A motorised rotating mount selects the target device, aperture, filter, or the photodiode automatically during the measurement sequence. The other samples are sealed in darkness using metal plates clamped around rubber o-rings when the conditioning beam is active.


  • 6 sample positions that can magnetically hold contact lenses or other samples, for example neutral density filters for system validation
  • 1 clear position for automatic reference measurement
  • 1 photodiode position with photopic sensitivity to allow the automatic characterisation of the conditioning beam
  • O-rings and metal plates on either side of the samples not currently being measured allow them to be kept in darkness
Carousel in the water bath
Carousel in loading position
IL7 Xenon lamp 250-1500nm
IL7 Xenon Light Source

Conditioning Source

The conditioning source is based on a Xenon short arc lamp. The UV-rich light of the lamp passes through a rotating wheel that can place 4 customisable and lockable iris aperatures into the beam to attenuate the overall intensity. The attenuated light then passes through a rotating filter wheel, which can hold up to 6 filters to further control the spectrum of the conditioning beam. The light is guided to the water bath by fibre bundle, where it is collimated and shone onto the sample from two directions. Further spectral modulation is possible by partially covering the fibre bundle entrance with another filter. The source also houses a shutter.

The conditioning source is powered by a Bentham 610 Current Stabilised Lamp Power Supply, a high power current source with excellent stability.


  • Xenon short arc lamp
  • Spectrum controllable with filters and iris apertures
  • Nominally matched to AM2 
  • Shutter


Nominal conditioning beam spectrum
610 lamp power supply
Both light sources in the system are powered by Bentham 610 stabilised constant current power supplies

Probe Beam Source

The probe beam originiates from a 250W quartz halogen bulb in a custom enclosure that also houses an optical chopper, and cooling fans. Like the conditioning beam it is powered by a Bentham 610 Current Stabilised Lamp Power Supply, a high power current source with excellent stability. This provides a probe beam powerful enough after monochromation to accurately measure the optical density, but which when spread across several mm2 is sufficiently diffuse to avoid activating the samples.


417T 5 detection electronics mainframe 5 unit configuration

Acquisition Electronics

The main transmittance measurement acquisition detector of the BPC300-C system is a DH_30_TE Thermoelectrically-Cooled Multi-Alkali Photomultiplier. The signal is recovered from this using a combination Bentham 477 AC current pre-amplifier and Bentham 496 DSP lock-in amplifier, precision acquisition electronics that can boost miniscule currents while discarding the DC signal from the conditioning source.

The photodiode in the carousel is measured using a Bentham 487 Picoammeter for precise determination of the incident beam intensity.

The modules are housed in a 417 detection electronics mainframe, together with auxilliary control modules, such as a Bentham 215 High Voltage Power supply to provide the necessary potential to the photomultiplier, and a Bentham 218M Optical Chopper & Control Module.


Control Software

The BPC300-C is controlled via USB by Bentham's BPC300-C measurement and automation utility Photobench, an add-on to Bentham's popular BenWin+ spectral analysis suite. Photobench controls the BPC300-C hardware, measuring each lens automatically and sequentially by a standards compliant process, or by a process defined by your scientists. Once the measurements are complete, Photobench calculates relevant photometric values for each sample by standards compliant methodology, and presents these to the user as a PDF report or a computer-readable XML file. 

The system maintains an audit log, optional user management and a permission system that allows you to create user accounts with restricted permissions depending on user roles independently from your main IT infrastructure, or simply BenWin+'s full set of features available without restrictions.


  • Standard USB control, no special computational requirements
  • Windows 10 compatible
  • Optional user rights management / audit log / XML file production for LIMS support
  • powerful spectral and colorimetric analysis features
  • photochromic parameters are calculated automatically
  • PDF output reports
Photobench main control form allowing sample definition, profile selection, and the ability to launch measure
Photobench Settings form showing how the measurement process can be customised.


BPC System and Software Photochromic Contact Lens characterisation BPC300-C
Liquid Calibration Standard and Holder On-Site recalibration of TMC300 Wavelengths, in-situ
IDR150 System On-site conditioning beam spectral measurement, immersed, at sample plane. Includes intensity-calibrated light source for absolute measurements.
Emissive Calibration Standard On-site recalibration of IDR150 System wavelength from atomic emission lines CAL_CL_HG
Deuterium Lamp Measurements below 280nm IL6
706 Power Supply Deuterium Lamp Power Supply 706
Alternate diffraction gratings Allows measurement of extended spectral range various, contact us with requirements
Alternate slit widths Enables measurements at different bandwidths various, contact us with requirements
Windows-based Control PC Drives hardware various, contact us with requirements

Measurement Process

More details on the measurement and conditioning processes are provided in the Measurement page.

Main bench-top assembly

Main bench-top assembly dimensions

Total Width 1500 mm
Total Depth 670 mm includes overhanging parts (rear)
Bench Depth 620 mm bench only
Total Height (max, open) 700 mm approximate
Total Height (closed) 400 mm approximate

Control Electronics

The BPC300-C contains a 417 electronics mainframe, and two 610 power supplies, all with the same external form-factor. Space for three control / acquisition electronics enclosures each matching the below specifications is required. These can be stacked on top of one another or arranged as space permits. They must be in physical proximity to the bench-top assembly.

Control electronics dimensions, per device (3× required)

Width 450 mm without handles
Width 465 mm with handles
Height 140 mm with feet
Depth 156 mm without handles, plugs
Rear space required 120 mm cables, ventilation
Front space required 60 mm for handles, cables

Measurement Geometry

Elements involved in the transmittance measurement.

To perform a transmittance measurement, the carousel is first rotated to a clear aperture for a 100% reference measurement.

The light from the probe source is unshuttered and mechanically chopped to produce an AC signal of known frequency. The light is shone through the probe source monochromator, which selects a 5 nm bandwidth band. The monochromatic light is collimated and shone into the water bath, through the clear aperture in the carousel, into the integrating sphere on the entrance of the measurement monochromator tuned to the same wavelength band, and into the photomultiplier. The signal from this is recovered by the acquisition electronics. 

By scanning the source and measurement monochromators across the wavelength range of interest, the spectral reference photocurrent can be measured.

The carousel is then rotated to the lens to be measured, and the measurement is repeated. The ratio of the sample to reference measurements yields the transmittance of the sample.

Conditioning Geometry

Elements involved in the AM2 conditioning of the sample

In order to simulate the effect of sunlight illuminating the sample, the light from a Xenon bulb is filtered, attenuated, and focused on the entrance of a fibre bundle. This bundle is split and both ends collimated and shone onto the same locations on the sample. 

During measurements with the bias light active, the chopped probe signal and measurement monochromator prevent the bright conditioning light from affecting the measurement. 

While the conditioning beam is active, the probe and measurement monochromators can be tuned to a single wavelength to measure the transmittance at that wavelength as a function of time. Once stable the monochromators can be scanned across the wavelength range to measure the spectral transmittance of the activated sample.

The carousel is rotated to a photodiode position at various points in the measurement flow to measure the intensity of the conditioning beam, to assure that it is operating at the correct intensity.

Measurement Results

Example Spectra acquired during a run of a BPC300 system

Measurement Reports Excerpts

Produce reports according to the calculation methodology prescribed in particular standards. The below examples are excerpts of the standard AS/NZS 1067:2016 report.

AS/NZS 1067:2016

Front page of measurement report for AS/NZS 1067:2016 including categorisation decision and other summary data
Basis of decision for categorisation, faded lens
Basis of decision for categorisation, darkened lens

Some standards also prescribe acceptable colour regions, such as ANSI Z80.3-2015, excerpt:

ANSI Z80.3-2015

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