Because the items are going to have to remain in close proximity, it's unlikely that there is anything that will completely solve your problem, but there are a couple of things you can try.
If the lights are wired, it is possible that the wire is working as an antenna, and you can use a Ferrite Choke or two on the wire.
Tape one near where the wire leaves the battery, and another to where the wire lead plugs into the light.
The can be found at stores like RadioShack for a few bucks.
If the lights are wireless, aluminum and tin foil is an excellent reflector for this kind of Electro-Magnetic Interference (EMI).
The first step would be to see if foil will help.
Try wrapping the outside of the lights with foil and repeating the tests you did before.
I doubt you can add foil to the computer because this will interfere with it picking up the wireless signal from the sensors.
If that reduces the interference you can tape the foil to the lights, carefully cutting away the foil around mounting brackets and buttons and see if the EMI is still reduced.
If the lights can be easily disassembled you can try taking them apart and lining the interior with foil as well; take care not to short out the internal electronics.
Good Luck.
bicycles.stackexchange.com/users/213/Gary.Ray
The problem is the current controller built into the LED bulb has no or ineffective EMC suppression.
This is extremely common in cheap equipment from unbrand named suppliers, who save costs by not going though the rigourous CE or FCC testing requirements.
They also cut costs by not placing components (usually a small cap is all thats needed), and lay out the board poorly so it radiates noise.
I have heard of people successfully soldering a small tantalum cap onto the LED board.
Best palce is as close to the control IC as possible, across the power input wires.
If that does not work, another across the LED itself would help.
(Careful, they are polarised)
Alternately wrap it in a conductor
(Tin foil is good), and tie it to ground to create a Faraday cage.
Problem is with it tied to ground, its hard to ride far, and you need a hole to let the light out, but that lets out the RF noise.
A better option is to buy a light that meets CE or FCC EMC standards, but they tend to be more expensive.
bicycles.stackexchange.com/users/3924/mattnz
I too had major interference problems between my 700lumen Smartlight (no, not the Garmin one, just a brand called Smart) and VDO M6 wireless computer with all 3 sensors (speed, cadence, HRM) stopping when light was on.
I tried wrapping the light in normal, household aluminium foil
and hey, it works!
Not too pretty but no need to spend time making a bracket to mount the light away from the computer.
By the way, it also started working, without the foil hack, when I held the light more than 12cm from the computer.
bicycles.stackexchange.com/users/29580/ian
When wrapping your light with tin foil, remember high power means maximum ventilation is required.
They can chuck out some heat.
On the computer side, when was the last time you changed the battery in the sender unit attached to the fork?
Does the problem only occur when your light is on flash or pulse?
If so try switching to a steady light instead.
bicycles.stackexchange.com/users/46569/Bernie Green
For me, foil allowed the computer to operate only if I covered the entire light, cord, and battery with foil, including the lens.
So, I got a new computer that uses signals from GPS satellites rather than pulses from a magnet on the wheel to measure speed and distance.
This solved the problem.
My light is a Nite Rider MiNewt.
It has a cord: it is not the wireless version.
My old computer was a Specialized Sport.
My new computer is a Garmin Edge 25.
I had used the MiNewt with other wireless computers without problems.
bicycles.stackexchange.com/users/29982/nanofish
Another thought is to disassemble the light, and paint the inside of it with electrically-conductive paint.
Downsides are that the light is more capable of shorting should anything go wrong with the internal wiring, and you might damage the light by disassembling.
You could also paint the outside of the light, but it would suffer from wear.
Note the paint used MUST be electrically conductive,
not just silver-coloured.
These paints are expensive, probably more expensive than a new light.
bicycles.stackexchange.com/users/19705/Criggie
My LED lights seem to be causing my wireless cycling computer to not pickup the signal (suggested by the manufacturer and verified through tests at home).  What strategies/options are there for reducing the interference outside of repositioning the computer (since I've tried all available positions)?
Stopping interference between LED lights and wireless cycling computer
bicycles.stackexchange.com
<bike-computer><led-lights>
bicycles.stackexchange.com/questions/1556
bicycles.stackexchange.com/users/30/curtismchale
To stop lights interfering with the computer follow these steps. If the lights are wired, it is possible that the wire is working as an antenna, and you can use a Ferrite Choke or two on the wire.  If the lights are wireless, aluminum and tin foil is an excellent reflector for this kind of Electro-Magnetic Interference (EMI).  The first step would be to see if foil will help.   I tried wrapping the light in normal, household aluminium foil. If that reduces the interference you can tape the foil to the lights, carefully cutting away the foil around mounting brackets and buttons and see if the EMI is still reduced.  However, a better option is to buy a light that meets CE or FCC EMC standards, but they tend to be more expensive.   There seem to be several options. In case the lights are wired, you could try taping a couple of ferrite chokes in the battery wire output and in the light input. In case the lights are wireless, on the other hand, try wrapping foil around the outside of the lights, except for the area around brackets and buttons. You could also try covering the lights' inside with foil. Fastening a small tantalum capacitor close to the control IC of the LED board, or adding a capacitor right across the board, might also solve the problem. Finally, you might consider using a computer operating with GPS satellite signal, or painting the lights' inside with electrically-conductive paint.
In case the lights are wired, you could try taping a couple of ferrite chokes in the battery wire output and in the light input. In case the lights are wireless, a good solution would be to wrap foil around the outside of the lights, except for the area around brackets and buttons. You could also try covering the lights' inside with foil. Fastening a small tantalum capacitor close to the control IC of the LED board, or adding a capacitor right across the board, might solve the problem. A possible, if more expensive, solution would be to only buy lights that meet CE or FCC EMC requirements. You might consider using a computer operating with GPS satellite signal, rather than magnet pulses from the wheel to avoid this issue. Painting the lights' inside with electrically-conductive paint might overcome this problem.