All of the lights I rock on my bike at present were designed for bikes. I have been slightly creative in how I have mounted lights, but not very creative in either fashioning my own lights or repurposing lights meant for other things.
We have featured some pretty creative light hacks over the years. A beach cruiser light was fashioned from scratch, our post on 5 Killer Looking DIY Bike Headlights has a sci-fi feel, I stumbled across a pair of glasses that were used as a rear light, someone submitted a picture of a tea tin light, and we have seen many flashlight hacks (see here, here, here, and here).
Reader Harry took some lights designed for a car and decided to give them a higher purpose. His text and pictures are below. When he wrote me I had a question about moving from watch batteries to a 9 volt and he kindly included information on that as well. If anyone has questions I am sure Harry would love to answer them in comments. All pictures and text credited to Harry.
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First find any LED set at a local auto parts store. Making sure you get the ones with the "test" button.
Also pick up a simple on/off toggle switch.
You should have something like this in the package. The small black box contains a stack of watch batteries that should last for quite a while. You must cut off the button and replace it with the toggle switch. ((I don't think you want to ride around holding a button down))
After replacing the button with the toggle it should look something like this.
Now comes the relatively easy part. Finding a place to mount the strip. Most have some form of 3M tape on the backside. Personally, I prefer to use zip-ties as that makes it a lot easier for removal.
But, when they DO wear out, I simply cut the wires and change that to a 9 volt connection for the 9 volt battery. It's still small enough to hide in a lot of areas on the bike but still provide plenty of long lasting power for the lights. Most people are only going to burn them for an hour or two on an occasional basis. But I ride with them on even during the day just for an extra safety "edge."