This system is designed to perform transmission tests on photochromic lenses as specified in EN1836:1997.
Lenses up to 75mm diameter can be tested over a wavelength range of 280nm to 780nm in the faded and darkened state.
A conditioning beam as specified in the standard is included. The conditioning beam can be set to 50klux, 15klux or switched off, all by the control software.
A thermoelectric heat pump, controlled by the PC, is used to set the temperature required for each measurement and maintain the sample temperature to within ± 0.2°C at the specified levels.
The system includes enhanced BenWin+ software which, amongst other things, will return:-
The rate of darkening and fading is also monitored at a single wavelength or over the whole spectrum if required.
The optical part of the system is mounted on an optical bread-board approximately 75cm x 45cm. The electronics (excluding the PC) is contained in a floor standing 19" rack.
Main System Requirements
The main points to be accommodated by such a system are as follows:-
1) The level of radiation in the analysing beam should be high enough to allow fast and accurate measurement of transmission, but not so high as to cause any measurable darkening of the lens during the measurement of the faded state.
2) The optical arrangement must allow for some optical power in the sample whether caused by non-parallelism in the faces of a plane sample or by curvature in a full lens.
3) The temperature of the sample needs to be controlled precisely, even when it is being irradiated at 50klux.
4) The ability of the detector to “see” light scattered from the conditioning beam should be minimised and in any case such scatter must not contribute to the measured ＆#118alues of transmission.
5) The spectral shape of the conditioning beam should correspond as closely as possible to the specification given in the standard (Moon, etc., section 6.1.3.1, EN1836:1997. Curve attached). It should be uniform over the region of the sample used by the analysing beam and it must be possible to vary the level without changing the spectral shape.
6) The light source, monochromator and detector must allow measurements over the spectral range 280nm to 780nm. The scattered light at 280nm must be sufficiently low to allow measurement of low transmission in this region.
7) The system should be fully automated requiring only that the operator inserts the sample and keys the computer to execute a predetermined sequence of measurements. Complete automation facilitates the addition of automated sample changing if required.
This Bentham system achieves all of the above. Contact us for a complete technical description of this impressive system.
