Homebrew rear Cree LED dynamo light


Newly Enlightened
Oct 12, 2004
cheltenham uk
I've just completed fitting homemade rear lights to both my dynamo hub rigged bikes using Red

CREE LED Emitters from Dealextreme.


Both of my frontlights have 3 White Cree/SSC LEDs powered by a simple smoothed rectifier circuit.

See circuit 2 http://www.pilom.com/BicycleElectron...its.htm#Basics and imagine 3

LEDS in series.

For reference my 1st light I made from the head of one of Kaidomains short run of triple Seoul

SSC P4 lights - http://www.kaidomain.com/ProductDeta...ProductId=1270

The second I bought from Saltytri -


I was quite happy with both lights which I also use in daylight for commuting but I was looking

around for a matching powerfull 0.5 or 1 Watt battery powered light for the rear.

If I were to put an additional Red LED in series run from the dyanmo I would suffer 2 distinct


1) Low speed lighting would be worse

2) A single point failure in the wiring to the back of the bike would take out both the front and

rear lights.

BUT RED Cree lights use less voltage than WHITE LEDS.

Saltytri's light already had an extra cable coming from it that you could use to short out one of

the LEDs for better low speed performance.

So I decided to short one of the front white LEDs out with a rear red LED.

They are made quite simply. I just bolted them to some stock aluminium with a heatsink (a bit OTT?) and then almost completely potted them with a clear epoxy mixed with either orange or red glow powder from glowinc.

Front before potting


Dynamo Backlight before potting by leofwhite, on Flickr



Dynamo Backlight rear by leofwhite, on Flickr

During potting


Dynamo Backlight whilst potting by leofwhite, on Flickr

The 3 position switch on my handlebars now has the settings :

Left = Medium Beam (1 Led completely shorted) for riding in a group

Centre = Full beam for riding on my own at night or downhill

Right = Medium beam plus rear Red Led running at 1.25 Watt for daylight commuting and fog (it's way, way too bright for riding in a group and paints the road behind me red.

After seeing the output that I'm getting I suspect that the 0.5 watt and 1 watt rear LED lights I've seen can't be driving their LEDs very hard. If they were their batteries would have a very short life.