LED Opal Diffuser Light Source
Research into LED and light properties determined that an opal glass diffuser would achieve a lambertian distribution as close as possible to ideal. The natural optical properties of the opal glass cause any incident light from a point source to disperse in a lambertian distribution. Three very small surface mount LEDs are used to provide a source (at a given wavelength) located about 10mm behind the diffuser. The opal glass attenuates the LED intensity, therefore three LEDs are required in order to provide sufficient intensity in the measurement cell. The LEDs are mounted on an aluminum heatsink which keep them from over heating and also provides intensity stability. The combination of LEDs and opal glass guarantee that the light source distribution remains stable, and that repeatability is consistently achieved.
LED light sources are found to be superior to the flash lamp light source due to:
- LED's emit light at a specific wavelength, eg 525nm, 450nm, 635nm thus no bandwidth filters are required
- A single light source can be constructed of multiple LED's and controlled to sequentially emit light of different wavelengths
- Only one PMT required as light source is sequential not simultaneous
- Sequencing of light source maximises the light's intensity as it eliminates the need to split light into three seperate paths
- The use of a single PMT eliminates the need to tune three seperate PMT's
- Life of LED's far outlast flash lamps, which are generally replaced yearly
- Heat generated by the LED light source is a fraction of a flash lamp, minimising changes in sample RH
With the introduction of the opal glass, the aperture of the light source window has been dramatically reduced to only 10mm x 13mm. This reduction in aperture has significantly improved the uncertainty due to angular truncation. The diagram below shows a cross section of the Aurora 1000 & 3000 cell without backscatter. The truncation angle is now from 9° to 171°, providing a full 162° of illumination.