The basis of the illuminator is a neutral white Cree XHP 50 module. At its maximum power of 18W it outputs about as much light as a 100W halogen, so it should be plenty bright.
The power supply is a dimmable constant current driver. Any supply with enough current will work, but I picked one that fits neatly into the cavity occupied by the original power supply of the microscope, so it does not have to be external.
The power supply is just narrow enough to fit into the back of the microscope, but the case has to be modified so that the wires come out the top instead of the sides. I simply filed holes into the case for this, and crimped the wires into a Molex 42022 connector that mates with the microscope's original wiring harness. Here are the new and old power supplies, side-by-side:
![Image](https://benedikt-bitterli.me/micro/illum/supply.jpg)
For cooling, I'm using a cylindrical heatsink. I wanted the heatsink to protrude out the back of the scope for improved cooling, and this heatsink is about the biggest you can go to still fit into the 47.6mm bulb opening in the microscope body. The heatsink is undersized (rated only at 10W) but I don't plan on running the LED at full power. The square PCB of the LED module is just a bit too wide to fit into the microscope's bulb opening, and the corners have to be filed down. The original LED module has friction fit connectors, but I removed them and soldered wires with a molex connector to it instead. Here are the new and old illuminator, side-by-side:
![Image](https://benedikt-bitterli.me/micro/illum/bulb1.jpg)
I designed a 3D printed attachment that holds the heatsink. It's designed to match the screw holes of the original tungsten bulb holder, and holds the module at the correct depth so that the LED sits at the same position in the microscope as the original filament:
![Image](https://benedikt-bitterli.me/micro/illum/bulb2.jpg)
The power supply is intended to be used with a dimmer, but an adjustable potentiometer will work too. After some experimentation, a 10K logarithmic potentiometer gives about the correct brightness range, and I found one with the correct shaft length to replace the original potentiometer in the microscope, so the light can be dimmed with the same knob as the tungsten bulb would. I added an additional 660 Ohm resistor in series so the brightness adjustment range "feels right", but that is optional. The potentiometer and series resistors are crimped into the original wiring with dupont connectors in case I want to adjust these components in the future:
![Image](https://benedikt-bitterli.me/micro/illum/potentiometer.jpg)
The original wiring was modified to connect to the bulb with a molex connector, in case I want to play with different LEDs in the future:
![Image](https://benedikt-bitterli.me/micro/illum/attached-bulb.jpg)
The power supply is attached to the back plate with double sided tape and mates onto the original wiring:
![Image](https://benedikt-bitterli.me/micro/illum/attached-supply.jpg)
The LED is plenty bright and even at its lowest power, microscopy is only comfortable with the neutral density density filter in place. I'm quite happy with it - the higher power is very useful for darkfield/phase contrast and when imaging with a camera. The finished product:
![Image](https://benedikt-bitterli.me/micro/illum/bright-1.jpg)
![Image](https://benedikt-bitterli.me/micro/illum/bright-2.jpg)
The heatsink runs a bit warm, as only part of it is outside and can rely on convective cooling. This is fine for now at lower powers, but I may modify this in the future for better cooling if I need higher power continuously.