I started with a typical bath fan/light combination unit already installed in my home. Most of these units are similar in construction and assembly.
Simply pull the grill & lens frame down slightly and you can access the torsion springs to fully release the assembly. Most have a simple plug like connector to disconnect the light kit. (Some older units, the lens will snap off and reveal a center screw/knob to remove the grill/light tray and disconnect the wiring.)
Once removed you find most have a simple steel or aluminum light reflector box. Most of the lamp sockets are simply snapped or screwed into these. We won't need it anymore, but you may want to save it for another project. So cut the wiring but leave a couple inches of wire so you can re-use.
I am using double row flexible LED strip at about 6watts a foot. The project is using only about 16" so I figure I'm less than 10watts. This is replacing a screw in CFL at 26watts or the original 100watt incandescent. Like wise I found a small 1.25amp 12vdc power supply(PS) small enough to stuff right in the middle.
The LED strip has 'sticky back' (double sided tape) so it goes down no problem after cutting to size. The power supply is simply put in with double sided tape. It may be more wise to drill some holes and use zip ties or fabricate another type of strap as it will be inverted when installed. I have faith in the tape and this was to be a test anyway so I left it at that. Also the PS weighs next to nothing.
Some of these unit use a molex type connector, others simply have a non-grounded outlet to plug into. Mine has the connector so I cut it off the original socket and crimped it on the the PS once I cut it's plug off. (with this type of connector the light tray is grounded as it should be, so I re-connected the ground wire to tray as mine was originally riveted on but broke off )
Once I fitted everything it was simply a matter of soldering a few wires to each strip and to the PS low voltage side.
A test run and... Nothing. I had had forgot to check the polarity of the PS and off course guessed wrong. No big deal, simply reversed the polarity and were all lit up! Brings up a point I forgot to mention. These LED strips are polarity sensitive, so attention should be paid to the wiring to keep it in order.
Plenty of light without the lens! Lets finish and see the result. I should have brought a light meter but from experience in my own shower I can say that the LED strips are a bit brighter than the CFL and just as good as the incandescent. This particular tape is close to 3500k so it's cooler color temperature also brightens up the area a bit more than the yellowish CFL(2700k).
Very pleased with the result. Project only took about 30minutes and cost about $30-$40 depending n where you source your parts.
Note: It is common for this type of power supply to have a slight delay each time it is turned on. So expect that you may have to wait one or two seconds for it to come on. Also as with anything within a certain proximity to water/bath/shower this should be on a GFCI protected circuit.
Sorry for the lack of pictures, this is my first insctructable and wasn't exactly planning on writing it...
PSA: This is a great time to remove the motor assembly and gently remove all the collected debris from the blade and motor. An old tooth brush works great for this, or compressed air. No one ever does this, but will extend the life of your motor and performance of the unit. Most of these unplug or disconnect like the light kit and may have just a few screws to release the motor/fan blade assembly. Do not lubricate the motor unless instructed by the manufacturer, most of these motors do not require lubrication. If you have to, a (as in one or less than one) tiny drop of light oil on the shaft, !!!DO NOT SPRAY!!! with aerosol lubricant!!! This is bad for electrical stuff typically, and death to many of these motors people bring to me to replace.