Full spectrum coverage with LED illumination
The fluorescence technique which is now much used in Life Sciences and Materials research requires intensities at multiple defined wavelengths. These systems also require precise intensity control with the ability to switch on and off quickly and repeatably.
Work to address both brightness and control has resulted in the development of a universal fluorescence illumination system, the pE-4000 which features 16 selectable LED wavelengths. This is considered adequate to satisfy most applications with intensities below 400nm where there is increased interest for in-vivo and optogenetic applications. Provision for subsequently incorporating lower wavelengths (such as 340nm which requires using special optical materials which transmit at UV wavelengths) was taken into account.
In order to offer a system with extensive functionality such as stability, fast switching-speeds and the ability to generate sinusoidal and square-wave functions, software communication via USB and TTL triggering via multiple BNC connections were incorporated. The ability to trigger in, trigger out, and operate under analogue control was incorporated. Switching speeds achieved under TTL are in tens of microseconds.
A complexity in developing an illumination system covering a wide spectrum is that losses incurred when combining LED light of different wavelengths can quickly compound and render overall performance unacceptable. However, it was recognized that optical filters used to separate excitation and emission channels impose limits as to how many illumination wavelengths can be used without cross-contamination between excitation and emission light. Further investigation identified that it was possible to group performance into four bands of mutually exclusive wavelengths.
Four motor driven LED modules were then designed, each supporting the necessary wavelengths for each band. As this optical design requires fewer combining optics, losses are dramatically reduced. The overall physical and environmental footprint of the system is reduced.
Wavelength Grouping Concept
Active air cooling technology ensures that the LED is held at a constant temperature. The LEDs can then be over-driven for greater intensity without causing damage. Cooling increases useable lifetime and ensures that output is stable over both the short and long term.
Application of phosphor technology has enhanced LED illumination systems by increasing intensity where LEDs are less intense. A phosphor which is excited by a powerful LED peak can be selected which emits at a wavelength where the LED is weaker.
The design of the pE-4000 has resulted in an intense, controllable and broad-spectrum illumination system which can be operated as a simple white light source or as an advanced research tool depending on the user’s requirements.