Fluorescent Materials

HH series instruments support a range of emitter complements and use a dual filtered detector. They can be configured to perform direct measurements of the concentration or strength of a specific type of fluorescent agent. With the current availability of LEDs emitting at 370 nm, we are able to configure HH series instruments to perform a direct measurement of "brightners" used in paper and textiles. These materials (e.g., Uvitex) have an excitation peak between 350nm and 390nm and emission peaks near 450 nm. By directly exciting the fluorescent agent and measuring the emission pea, while excluding the excitation energy, we are able to perform a direct measurement of the effective strength of the fluorescent material.

This performance is achieved in a low cost, high reliability hand-held instrument with full color measurement features.

To the first order our procedure is different from the procedures classically (TAPPI, ISO) used to measure brightness, which attempt to measure apparent reflectance in presence of an unknown concentration or strength of fluorescing agents with either minimal excitation energy or an adjusted level of excitation energy. TAPPI (e.g., T 452 OM 92) methods were designed to measure the effectiveness of bleaching and did not account for the effects of, or use of, fluorescent materials to transfer optical energy from the near ultra violet region to the blue region of the spectrum. These procedures specify delivery of minimum levels of energy to the sample in the excitation region. (Specifically, illumination at a 3K black body temperature). The visual whiteness or brightness of materials treated with fluorescent "brightners" is a function of the strength of the fluorescent material, the energy available to excite the fluorescence and the "standard" (non fluorescent) reflection of the material. ISO 2470:1999 suggests that modern instruments may be adjusted by varying the ultraviolet content of the illumination to generate ISO-defined brightness conforming to a specific standard. This is required because the relative UV content of illumination varies from instrument to instrument.

In HH series instruments we illuminate with a known and stable amount of energy at each wavelength. In an instrument configured to measure the strength of a specific fluorescent agent we filter the light reaching the detectors, so that we differentiate the response between the excitation peak and the emission peak. This allows the measurement of both the non-fluorescent reflectance spectra and strength of the fluorescent agent. In the use of HH series instruments in that application we assume that only one type of fluorescing agent is present. If multiple agents are present, we suggest the use of our dual mono TT series model 2000530.

The first two instruments of this series are a windowed 12 mm 45/0 colorimeter (model 2000470 with optics equivalent to 2000420), and a 3 mm 45/0 (model 2000471 with optics equivalent to 2000430). The excitation peak is 370 nm and the excitation / emission cutoff is 420 nm. The list price is $2,950, including a Colorimetry II equivalent memory card. Direct strength measurement is supported in portable mode and other functions are also supported by AccuWinSoftware.