as well as scientifically useful visual effects can be obtained by
employing colored LEDs instead of the normal
lamp ﬁtted in the lighting assembly in a microscope base. Of course, the
lamp can be simply replaced by a white LED
with appropriate changes in the supply current/voltage etc., but it is
more interesting to have three colors available — here, red, green and
orange (amber) which are individually adjustable for intensity. The
dashed line around LEDs D2, D3 and D4 indicates that they are ﬁtted in a 10 mm long section of 1-inch plastic (PVC) pipe.
The 5-mm holes for the LEDs are drilled at an angle so that the LED
beams are pointed downwards at the center of the holder. As shown in
the photograph, as small piece of veroboard can be ﬁtted under the ring,
with a 1-inch hole in it so that the centre of the ring remains open,
allowing the assembly to be placed on top of the glass specimen carrier.
The PCB, which is held secured to the ring by the LED wires, allows wires to be run between the lighting assembly and the driver electronics ﬁtted in the microscope base.
The white LED, D5, takes the place of the
(6-V) lamp in the lamp holder, and is connected to the driver circuit by
wires. The potentiometers P1, P2 and P3 allow the intensity of each
color to be individually adjusted, while P5 acts as the master intensity
control. Space allowing, the pots may be ﬁtted in the microscope base.
If there are problems with reﬂections in the ring, paint the inside
black. Finally, in most microscopes there is a need for strong lighting
which pleads for high-intensity LEDs to be applied in this circuit.