OptoLED high stability light source
Light Emitting Diode (LED) technology has been progressing rapidly in recent years, to the extent that LEDs can now replace conventional light sources in many applications. New developments have yielded devices that are both brighter and capable of operating at shorter wavelengths than their predecessors, and this trend seems set to continue.
In response to these technological advances, Cairn has developed the state-of-the-art OptoLED LED light source; offering a combination of high intensity, ultra-high stability and rapid modulation. Whilst the OptoLED is primarily being used with Cairn's fluorescence imaging and confocal (Programmable Array Microscope) systems, its modular design makes it a valuable general-purpose laboratory tool. We see it offering significant benefits for voltage sensitive dye studies, where stability is vital, and for extended timecourse experiments where long term stability and reliability are important. Preliminary tests also suggest that transient double or treble pulsing of LEDs might make it a useful tool for Particle Imaging Velocimetry (PIV) in conjunction with our Optosplit image splitter and an Electron Multiplied (EM) camera.
Don't just take our word for it though! 'Laboratory News' magazine placed it on the front cover of their February 2006 issue as their 'Product of the Month'!
The OptoLED power supply can drive two LEDs independently at currents of up to 10A. The drive current for each LED can be set either by a front panel control or by an external control voltage. If this control voltage is modulated, the output from the corresponding LED can be changed within a few microseconds, and a still faster (sub-microsecond) modulation can be achieved using digital control inputs. Independent digital inputs are provided for each LED and these can be configured with opposite polarity so that a single control pulse can rapidly switch between two different LEDs. When an LED is modulated on timescales longer than a few milliseconds, the junction temperature may vary significantly during the pulsing cycle, and this can in turn affect the optical efficiency, causing the optical output to vary during the on periods. Since such an effect may be undesirable, the option of optical feedback is also provided, which will fully compensate for this. The optical feedback is effective for both analogue and digital modulation, and its fast response time means it can be used in conjunction with LED modulation on a sub-millisecond timescale.
The functionality of the system is further enhanced by a digital meter, which can display the current and power levels of each LED independently. The peak and average LED power dissipation can be limited using presets on the main control board to protect the devices from being overdriven. This allows LEDs to be transiently boosted, to achieve higher instantaneous optical energy, while remaining within their thermal dissipation limits.
The LEDs are mounted in compact remote modules, which include a photodiode control board for optical feedback, and have a built-in aspheric condenser lens with focussing ring. Devices are available with wavelengths right across the visible spectrum and down into the near ultraviolet. Two or more LED modules can be combined using adjustable dichroic combiner cubes, and couplings are available for all popular epifluorescence microscopes.