BPC300-C Photochromic Contact Lens Spectrophotometer

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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.

Capabilities

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.

Components

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 0-50klx Shutter 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

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.

Monochromators

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.

Features

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.

Components

TMc300 Single Monchromator (x2)

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

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.

Features

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

Carousel

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.

Features

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

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.

Features

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

Components

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.

Components

ILD-QH-CHOP-24 housing
610 Current Stabilised Lamp Power Supply

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.

Components

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.

Features

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.

Options

Component	Purpose	Code
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

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

PhotoBench_User_Manual_v1.3.pdf (2.27 MB)

The Bentham Standard

We’re with you from the first call to the final result

Call us on +44 118 975 1355 or email us

BPC300-C Photochromic Contact Lens Spectrophotometer

Capabilities

Control ambient conditions

Perform detailed measurements

Set multiple measurements going at once

Leverage existing standards

Components

Features

Components

Features

Features

Features

Components

Components

Components

Features

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We’re with you from the first call to the final result