First I cast a layer of casting resin on a sheet of glass and laid a light layer of glass onto it. Once this had set I added the lights on top and bonded them in place with another layer of glass as you can see in the photo above.
Here are the lights ready to install in the shell. All four of them together weigh in at just less than 30 grams. They consist of three 2 watt LEDs in each light. They do get quite hot so that is the reason for the extra metal bit they are bolted to. It acts as an additional heat shink and allows air to circulate around the LEDs. I originally considered just casting them in resin but they get a bit too hot for that as their temparture gets close to the HTD point of the resin. If they get too hot they will have short service life. This all seems quite a bit of trouble compared to just bonding in an off the shelf LED as is found on most velos. The reason is that I don't consider these other lights adequate in all circumstances. They are not very visible in full sunlight. These new lights are hard to look at from less than about 10 feet and are very visible even in full sunlight. Another advanatage is that with a bit of extra work they can be mounted flush on the shell. They draw the same amount of power that our present turn signal lights with 18 LEDs in them use. Here is how they look once bonded in the shell with a bit more resin added to make them flush.
The better way to do it would be to make a mould so you cast the light with a little spigot sticking out that would fit through the hole in the shell. Then you mask around the sticking out part and carefull sand it off to match the shape of the shell. Sand to 1000 or even 2000 grit and polish. Once you had done a few you could probably get the sanding and polishing down to five minutes or so. This would also allow fitting to almost any velo.