Introduction: CFL Headlight and Taillight for (Electric) Bicycles

"Electric" is parenthetical because the CFLs (Compact Fluorescent Lamp) need a high enough DC voltage to start, and carrying a battery that big around on the bike isn't practical unless you already need it to run a motor. ;-)

Many CFLs will run on as little as 28VDC, once they startup, but may take 44VDC or more to get them started.    The key is to find CFLs that say 110-240VAC, 50/60Hz for their input.  If they just say 110VAC, 60Hz, they probably don't have the right electronics inside to work without modification (which is outside the scope of this instructable).  In areas that use 110-120VAC household voltage, you should be able to use the ones sold where you live at around 44 to 60VDC.   In areas that use 220-240VAC, it's probably going to take *at least* 70VDC to run the ones sold in your area.  The best part of them is that they will only use about 150-250mA, so total power consumption for the light they give is very low, especially for the price. 

As with any other glass item, you should be aware that if you ride your bike where you expect big bumps or potholes, it's possible for the shock to break the glass tube off the base if you don't have any shock absorption for it.  I don't cover making that, but it's possible to do.  It's probably better to just use some other more solid-state form of lighting, even if it's more expensive--you probably need the better beam/spot those would provide, too.

This instructable assumes a typical road-bike scenario, in which the main purpose of these lights is for *others* to see *you*, not necessarily for *you* to see *by*, so you don't get run over in traffic despite obeying all the rules and watching out, simply because someone didn't see you in the dark.  With these, if they say they couldn't see you, and you're riding where and how you should be, they probably ought to take off the sleeping mask before driving.  :-P

There is no specific parts list, as you'll be scrounging the items according to what's available to you, with the exception of the type of CFL noted above.  

There are some additional modifications you can make to the bulbs if you really need a little more voltage headroom, but I don't recommend them unless you're absolutely sure of what you're doing.  Those aren't in this instructable, but are documented on my e-bike project blog at  if you are really determined.

The photos taken on the carport are first with just the bike lights, then with the overheads on, which are four 4-foot 40W fluorescents, then with the bike lights off and overheads still on, so you can see some relative brightnesses.  My camera does not let me set the exposure time, even in it's "manual" mode, so you will want to note the difference in brightness of relative lights when comparing images.  In one of the yard pics with the dogs, it used a one second exposure time which resulted in a lot of blur but gives a very good idea of what this looks like in person. 

Step 1: What You'll Need:

Tools you need are:
Multimeter (even the cheap Harbor Freight DMM is fine)
Soldering iron and solder
wire cutters
wire strippers
needlenose pliers
Dremel or other cutting tools are handy
Drill, bits, etc.

Optionally you may need whatever tools your bike requires for adjustments, disassembly, etc, if you have to take anything apart or adjust it to make room for these lights, and/or to install them on the bike.

If you have an electrric bike, you'll need to make a splice into the output from the battery pack, preferably *after* the fuse or breaker that feeds your motor controller.   I recommend using the same kind of connectors already on your pack, and making a Y-splitter that can simply be plugged in between the pack, controller, and this new lighting setup.  If you bought yours as a kit, get the connectors from the same place if possible--this will ensure they are the right ones, if you dont' know a lot about this.  If they offer a Y-cable already, get that.

If your battery pack is less than the voltage required to start the CFL (call it 48V) then you will also need a way to boost that a bit.  Interestingly enough, laptop wall adapters/chargers and celphone wall chargers often work on 36V ok.  The only wa

If all you have is 24V, you may not be able to do this without making a battery pack specifically to put in series with your "traction pack" (the main motor power battery, as most of the adapters I've tried won't start on 24V or less, and aren't stable at their regulated voltages at that low an input.

If you don't have an electric bike, you'll need to get or make a battery pack that is fairly high voltage.  I don't cover it here in the instructable, but if you do it, be careful, as there are potentially dangerous amounts of power available in a battery pack with 40+ volts in it, even if you make it out of AA batteries, depending on what goes wrong (because something always does eventually, for somebody).

You'll need at least two CFLs, of the 110-240V 50/60Hz variety, preferably in a "60 Watt equivalent" size.  You can use larger or smaller, to fit your desired brightness, but that's what I used.  Mine are GreenLight brand, bought at the Phoenix, AZ "99 cent" stores.  At the time they were being sponsored by APS (local power company) at only 59 cents each!    I got them originally for the house to save money on electricity (it makes a significant difference).  

If you can, find some cheap ugly lamps you won't mind taking apart at a yard sale or thrift store, and try not to spend more than a dollar on each one.   All you are going to save out of them is the bulb socket.    It is best if they don't have a switch *in* the socket, but rather a separate one on the cord, or a chain pull for those hanging lamps.   If the cord is in good shape, all the better, because you can reuse the wire from it, too.  If it's frayed or cracked or old-looking, recycle the wire with the rest of the lamp.    You can buy sockets from the hardware store, too, but where's the challenge in that?

You'll need something to put the lights in on your bike.  For the headlight on mine, I used two cups that nest neatly inside each other--a styrofoam white one (because it reflects a lot of light and lets less thru than a thin white plastic cup would) from Denny's and a tough thick plastic outer one from QT.  Those were picked more because they were laying around than any other reasons besides those stated.     For the taillight, I used a taillight assembly off a dead Honda scooter from the 80's, mostly because the CFL would light it very well and thoroughly, and it is already a tough, water-resistant DOT-approved shell.   (I'm sure the approval is nulled by not using the lamp and reflector that came in it). 

For the taillight, you could use any kind of item or box that will help aim the light behind you, covered in red cellophane or party wrap, if you had no other way. :)

For the headlight, you could also use one of those clamp-on lamps with the large aluminum parabolic reflectors, often used for reptile and small animal habitats for heat lamps.   Depends on how much "throw" you expect from it to see by at a distance, rather than just using it to be seen by and for close-up vision.

A way to secure these to the bike is necessary.  I am still working on a good headlight mount (and a better housing), so the headlight is just taped in place with wraps of packing tape for now.  The taillight is securely bolted to the rear plate I already had an LED taillight on before, which had been transplanted from my original DayGlo Avenger bike to this CrazyBike2 early this year.

A roll of duct tape is fine if you don't care how it looks. ;)

Step 2: Testing the CFLs

The easiest part of this is verifying your CFLs will work with your battery.   Take one of the lamps you acquired and screw in the CFL to the lamp socket.

Don't plug it in the wall, because you're going to instead test it on the bike battery.

Here I have to assume you've found the best way to splice the power tap into the battery output wires, in a safe way.  You should have this tap fused, or breakered, so that if you accidentally short something you don't destroy your (expensive) battery.

Ideally, you could test this with a variable voltage power supply, but most of you probably don't have one.   I used a Sorenson 60V 1.5A variable voltage variable current-limit lab supply, because it was given to me and I found it fortunately and unexpectedly trivial to repair.  All I had to do was set it to my nominal battery voltage, then clip test leads from the Sorenson's positive and negative outputs to the lamp socket wires, at which point I found that on mine, 36V was not enough to light up the lamps reliably--sometimes they would start, but usually not.

If I dialled the Sorenson up past 42V they'd light most of the time, and at 44V every time (though it took a few seconds if it was too cold, in the 40's F).   That meant that most of the time, my battery pack even fully charged wasn't going to light them up, and I wasnt' going to add more battery to make this work.   Instead, I added a celphone charger.

The celphone charger, like the CFLs, can run on medium to high voltage DC, and still output it's rated power, up to a point.  It gets hotter than when plugged into the wall, so won't likely last as long.    It also only outputs 5.3VDC, which is barely enough to start the CFLs if the battery is very low.  So after a day or two of running it that way, I moved up to a laptop AC adapter/charger, to give 19VDC of headroom, which guarantees to start the CFLs as long as the batteries are anywhere above or at their safe lowest operating voltage, with room to spare. 

It is very important that the charger or adapter you use be "isolated", meaning that either of the flat blades of the AC cord or connector are electrically connected to either of the output pins/wires of the charger/adapter.   If they are not isolated, you cannot connect them in series as you'll need to do if you have the same problem I did.  You'll need to know how to use a multimeter to test for continuity, to test the above.

Assuming yours does not start correctly, then you need to find some chargers/adapters that meet the above requirements. Not all chargers/adapters will run on lower DC voltages. Just like the CFLs, they must be labelled with 110-240VAC, 50/60Hz, or they will probably not work.   Even if they are labelled this way, they may not work with your pack voltage, just like my CFLs didn't above. 

The first charger I found to work was an Averatec PA-1650-01, capable of 19VDC output at up to 3.8A.  It stays regulated to 19V down to around 29VDC input, though it takes at least 33VDC input to start it properly, and it takes up to 5 seconds to actually start outputting anything from the time it's plugged in.  
Apple Powerbook chargers (which would be nice, with their 24VDC output) don't work on my pack voltage, though they probably would on 48VDC or higher.

The AC adapter test setup is shown in the diagram; if you have a spare wall outlet laying around not hooked up to anything, you can use it attached to your battery pack to plug in each adapter you want to test so you don't have to deal with cutting and splicing wires just to do each test.  Makes it easy and non-destructive, since each adapter that doesn't work for this you can just put away for whatever future use you may have for it.

Assuming the CFLs wont' start, you'll wire in the ac adapter as follows:
--Pack negative to CFL base screw and to charger/adapter AC input pin (either one).  
--Pack positive to charger/adapter AC input, other pin. 
--Charger/adapter DC output negative side to pack positive. 
--Charger/adapter DC output Positive to tip of CFL base. 
--If there is a ground pin on charger/adapter's AC cord, leave unconnected-it probably is connected to the negative output or the shield (if separate) on the DC output side, based on the chargers I have here.

That means anytime the laptop adapter is powered by the pack, it will add it's voltage to the pack voltage, and that total voltage is what will be supplied to the CFLs, allowing them to start and run properly even if your pack voltage wouldn't normally allow that.  

With so little load on it, the laptop adapter won't likely draw much power--both my CFLs *and* the adapter draw less than 400mA at full pack charge.

Step 3: Building Up a CFL Taillight

This part is more DIY-on-your-own, because your setup is going to be different from mine; I just scrounge whatever I have in order to do what I need, so I can't really give a list of specific hardware to use for this.

However, it is helpful to have a screw-in lamp socket from old lamps, or buy them at the hardware store if you must.   Saves on trying to get wires soldered to the bases of the CFLs, since that is difficult for the screw-base part (it's often doesn't solder well due to the metal types used).

As an example, I'll show how I did my taillight.  I started with a ceramic-style lamp socket from an old broken  hanging lamp, which had a separate pull-chain switch (which isn't used in this).   As it was a screw-terminal type, I simply unscrewed the AC cord wires, and screwed on some wire saved from an old vacuum-cleaner AC cord.  I chose that wire because it is generally durable, and can take more of a beating than most other wire I happen to have laying around here.

It is far larger gauge than is necessary for the small currents needed here, but it is rated safely above the voltage to be used and is double-insulated.  That's a good thing since this is some fairly high voltage being fed along the bike frame to the CFL, on the order of 60+ VDC.  Not something you want to short against the frame and shock you.

Preparing the taillight housing, which was salvaged from an 80's Honda internal-combustion scooter, required a Dremel to grind away some metal, and a drill with a large bit.  However, a hand file and a utility knife would have worked, just taken longer.

The housing is simply held together by two philips-head screws.  Once removed, the clear red cover is set aside, and the reflector inside the taillight must be taken off so the old automotive bulb socket can be removed.

Since it is put together by a fold of metal from the socket lip around the base of the reflector, I used a dremel and grinding tip to remove the lip, so that I could pull the reflector off.  That then let me pull the socket out of it's housing (difficult due to the rubber gasketing).  

Once the socket was out, I had to cut a hole in the base where it used to be, large enough to accomodate the entire CFL ballast/base, as the bulb is too long to fit entirely inside the housing.  

My trusty old B&D drill, with an addon to hold much larger shank bits (as well as give me a hand-grip for it and gear down speed for torque when needed), let me use my panel-hole Unibit to cut the hole almost the size I needed.   

Then I used the unibit by hand to trim off some more edges of the hole (taking it out of the drill and using it as a scraper).  A utility knife will also work, but it takes out different shaped chunks, and the Unibit can be used to scrape circularly.  

Once the hole was made to exactly fit the CFL base, I inserted it in friction-fit from inside, screwed on the clear red housing, and tested it for brightness and internal temperature (as CFLs don't live as long inside enclosed housings).  I

Brightness was quite high.  It is enough to clearly light the wall several feet away reddish, even with the overhead 4-foot fluorescent fixture with a pair of 40W tubes in it.   Without the overheads, it is still enough to clearly light the room, and be able to easily distinguish things, read labels (and meter displays), etc.  

It is easily as bright as some cars' taillights are when they also have the brake light engaged.  No one should have a problem seeing this light, and it radiates not just directly behind as an LED light, but all around behind, including to the sides.  

I sealed the CFL in place with a bit of Gorilla Glue, as I don't have any silicone handy (which I'd prefer).  

Temperature inside the case next to the CFL glass is around 120-130F.  High, but not too high.  Cooler than it was with the automotive bulb inside, which was around 145F, for much much less light.

Step 4: Mounting the CFL on the Bike

I had already had a light mounted back there before, with a large aluminum plate to secure it and my LED brakelight bar (salvaged from a junkyard) to my cargo pods, so all I had to do in this case was to remove the existing taillight, create a hole large enough for the CFL base and socket, and install the taillight to it.  Coincidentally, two of the existing holes from whatever the plate was salvaged from lined up with the mounting screws for the taillight, saving me from having to drill new ones.

If you salvage your taillight from something else, you may also be able to use it's mounting hardware to bolt it to your bike.  If not, fabricating a mount is generally not that difficult but may require metalworking tools. 

Routing the wiring from it should be done carefully and in a way that guarantees it can't get snagged in your spokes, brakes, chain, etc.   Zip tying it to the frame is a good idea, at least every 8-10 inches, with no slack unless you have a pivoting frame for a rear shock, and then only just enough slack to not be taut when the shock is compressed or extended fully. 

You'll probably want a good way to turn them on and off; I use the controls of the same Honda scooter for my turn signals, horn, and headlight/taillight.  It doesn't have just an on-off switch for lights, but it does have a high/low beam headlight switch, easily repurposed to simply do nothing for Low beam but to switch both headlight and taillight on/off (by connecting/interrupting the return line from AC adapter + CFLs to the battery) at the same time. This switch is not actually rated for 60V, but I pre-tested it with over 120VDC using all my SLAs in series, plus a resistive load, before using it with the CFLs.

  Your switch can be anything that is rated for the DC voltage you will be placing across it, which is going to be whatever voltage you are providing to the CFLs.   It is important to use a switch rated for that voltage in DC, not just AC, or it could potentially weld the contacts together (highly unlikely at these low currents, but if something failed dead short, then assuming you have no breaker or fuse, it would take the entire pack current capability across it and that would probably destroy an AC-only rated switch).  

As for mounting the lights, sometimes it is possible to just get away with taping them on, if you don't mind the look of it. :)  My headlight, still built out of two cups nested together with the CFL in the bottom of them, is still just taped on the front stem, until I come up with the parts for a better reflector and focusing assembly. :)   Some pictures of it as it is now, with pedal reflectors taped onto the sides for side-marker lights, are attached below with the rest.

In the photos of the taillight below, the flash was used, and it's about two feet away from the white-painted inside of the back door, so this also shows how bright this light is.

The blog for the bike project as a whole is here:
with CFL-lamp specific pages here:

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