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LED Illuminators
for Microscopy & Instrumental Insemination

A recent development in Light Emitting Diode technology (LED) has resulted in some high brightness devices that have a white emission colour.

Clusters or arrays of these devices can be used as "cold light" illuminators for microscopy and instrumental insemination.
White LED The device itself is available in 3 mm and 5 mm standard LED packages, although it appears that the brightest only occur in the 5 mm style. Price was a bit steep when they were first introduced, but at the moment in UK the cost has fallen to a few pennies.

Single devices are adequate for II if they are close to the aneasthetised queen. A cluster of three will provide a wider field of illumination.

A cluster of seven would appear to provide more light than is really required for Insemination purposes, but may well be OK at low magnifications for use with a compound microscope. High magnification compound microscopy may need clusters of nineteen or more. At first sight this may appear costly, but if compared to the available fibre optic illuminators it looks to be a good deal.

Whilst these devices do not emit heat along with the visible radiation they do get hot if over driven. I will have to investigate this by building a prototype cluster of seven and making some measurements. If this heat is noticeable, the devices could be mounted in an aluminium block with fins and drilled holes for fan cooling, but this is a bridge that can be crossed when and if required.

The use of ultrabright coloured LEDs in arrays that contain more than one colour of emission, in conjunction with variable duty cycles, gives a very wide range of possible illuminating colours, that may have extra un-envisaged uses in compound microscopy.

Maximum intensity is realised by pulsing the device into the overdriven range... A 555 driving an emitter follower should be adequate, but watch out for RF interference from the 555.

Generalised Specifications... for bright LEDs taken from multiple sources.

Typical Values Forward Voltage
VF
(Volts)		 Reverse
Current
IR
(µA)		 Optical Power Output
PO
(mW)		 Brightness
(candela) 		Power
Dissipation
(mW)
Characteristics (@ 25°C)
    Color
 Min.Max.Typ. Typ.Max.Typ.
  Bright Red
 1.72.0??0.640
  Ultra Bright Red
 1.71.9 ?1.2-1.850
  Blue
 3.64.050.06.03.0?
  Green
3.54.0 50.04.010.0?
  Bright Yellow
 2.02.3  2.3?105
  White
 3.64.050.04.05.6?
Electrical Conditions
 IF=20mA VRev=5V IF=20mA

Absolute Maximum Ratings (Ta=25°C) Forward
Current
(mA)		 Pulsed Forward
Current
(mA)		 Reverse
Voltage
(V)		 Power
Dissipation
(mW)		 Operating
Temperature
(°C)		 Storage
Temperature
(°C)
Blue IF=30 IFP=100 VR=5 PD=120 Topr
-30 to +85		 Tstg
-40 to +100
Green
White

Colour temperature - White...   8000° Kelvin
Wavelength of Blue...  470 nanometer
Wavelength of Green...  525 nanometer		 Wavelength of RED...  645-700 nanometer
Pulse Width... 10ms, Duty cycle... 1:10

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Originated... August 2001, Revised... 07 October 2001, Revised... 09 September 2003,
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