How to install a LED and heatsink into a Mag-Light
Steps to install a LED into the Mag-Lite
The design sketch below shows how the heatsink slug fits inside the D cell sized Mag-Lite and how it is used. The text is is the same colour as the part drawn in the sketch. This works best inside a D cell sized Mag-Lite due to the larger battery tube having more room for the light to reach the lens and also more room to install a LED Genie which can then protect against overheating. To make the light water proof just follow the steps in this guide to making a DIY dive light.
NOTE: It may be possible to use the existing switch hole for gluing in a Piezo switch and then you can use the threads and o-ring that are already on a Mag-Lite (less work needed to modify) allowing you to change the focus/zoom of the light during a dive. I believe this will be possible to do, however I don't like the idea of moving single o-ring sealed parts under water as it only takes a grain of sand to get under the o-ring and you have a leak. If you choose to have a play with doing that then please let me know the results after 50+ dives so I can update this page on how well the standard o-ring performs.
This picture shows the heatsink slug inside the Mag-Lite battery tube. Just needs the LED star mounted with thermal glue to the flat surface. If you want to upgrade the LED, just use some heat to soften the glue, wipe and sand any excess glue off and glue the new LED star onto the same heatsink.
Why make your own LED when MR16 LED globes are sold in shops?
To cool an LED in a high powered dive light you need to transfer the heat from the small LED to the larger body of the dive light so that the water can keep the light's body and hence the LED inside cool. LED's create more light when they run cooler and can be permanently damaged if the LED temperature rises too high. It is for these reasons that an effective heatsink that fits tightly and has a good surface area in contact with the light's body is needed if you are to get the full potential out of any powerful LED. Ready made globes that are sold in shops that are MR16 drop-in replacements simply are not running to their full potential as they are designed to run below their rating (creating less light) in order to stay cool with nothing but minimal air cooling. If you want a bright LED, you must create your own with the best heatsink to transfer the heat into the water. You also find that ready made globes do not come in narrow <12 degree models, a narrow beam helps you to see further through the water. The pictures below show the heatsink's that I custom make to fit any LED mounted on a star to cool it effectively inside a Mag-Lite. Only one is needed, the photo shows you one from the side and another from the end which is drilled out to reduce the weight.