closetelectricallightinglow-voltageswitch
I'm hoping to put some lights in a residential hallway closet, so it's easier to see inside. I am considering running low voltage lighting (eg. these LV pucks), or a small regular-voltage light fixture or light socket.
What are the technical and code considerations for running LV vs. regular lights in a closet? Is it just a matter of personal preference, or is one way easier to do and/or more power efficient than the other?
For the record, I’d like to put the lights on a switch.
TL;DR: the dimmers aren't switching off completely: they're allowing some current to leak through, which is why you're seeing a voltage across the CFL. A different make of bulb may behave better with the leakage current that you're getting. Or perhaps a different brand of fan (if you haven't installed them all already).
I do know that operating CFLs in those sort of conditions will shorten their lives considerably, so you might actually be cheaper for you to use incandescents instead (a quick calculation says about 12 kWh per year for a 60 W bulb).
Read on for the technical explanation...
The voltage across the bulbs, Vb is determined by the formula:
Vb = Vin * Rbulb / (Rdimmer + Rbulb)
where:
The dimmer is a solid-state electronic circuit, so it has a very high effective resistance -- 10s of megohms is not unreasonable. Ditto for the control circuitry in the CFL. An incandescent bulb is a simple piece of resistive wire; a 60 W / 120 V bulb will have a resistance of 240 ohms.
Now, suppose the dimmer has a resistance of 50 MOhms and the CFL has a resistance of 10 MOhms; plugging the numbers into the equation above gives you 20 V across the bulb. OTOH, the voltage across a 60 W incandescent bulb will be about 600 microVolts, nowhere near enough to make the bulb glow.
If you have two bulbs in the light fixture, the resistance, R, of the two in parallel is given by:
R = R1*R2/(R1 + R2)
So if you have a CFL and an incandescent installed, the effective resistance is going to be very close to that of the incandescent alone:
R = 10,000,000 * 240 / (10,000,000 + 240) = 239.99 Ohms
Again, not enough to turn on either bulb.
With two incandescent bulbs, the effective resistance is half that of a single incandescent, so you have half the voltage across them.
The flickering you see with two CFLs is because the light you see is basically a high-voltage spark through the tube. The CFL contains circuitry to amplify the incoming voltage up to the point where the spark can occur. Under normal circumstances, the input voltage is enough to cause this spark 100 or 120 times per second (depending on mains frequency), which is far too frequent for the human eye to notice. With the reduced input voltage, it takes longer to reach the required voltage, so you notice the flicker. No two bulbs will be exactly identical, so they'll flicker at different rates and take different times to recover between discharges.
I was not able to find any sections in NEC that prohibit switches from being installed in closets, so until somebody can point to a specific section I'd say it's not a problem. There may be adaptations to the code in your local area, so you'll have to check with the local Electrical Inspector to be absolutely sure.
The NEC does, however, have a section on luminaires in clothes closets.
NEC 2011
410.16 Luminaires in Clothes Closets.
(A) Luminaire Types Permitted. Listed luminaires of the following types shall be permitted to be installed in a closet:
(1) A surface-mounted or recessed incandescent luminaire with a completely enclosed lamp
(2) A surface-mounted or recessed fluorescent luminaire
(3) Surface-mounted fluorescent or LED luminaires identified as suitable for installation within the storage area
(B) Luminaire Types Not Permitted. Incandescent luminaires with open or partially enclosed lamps and pendant luminaires or lampholders shall not be permitted.
(C) Location. The minimum clearance between luminaires installed in clothes closets and the nearest point of a storage space shall be as follows:
(1) 300 mm (12 in.) for surface-mounted incandescent or LED luminaires with a completely enclosed light source installed on the wall above the door or on the ceiling
(2) 150 mm (6 in.) for surface-mounted fluorescent luminaires installed on the wall above the door or on the ceiling
(3) 150 mm (6 in.) for recessed incandescent or LED luminaires with a completely enclosed light source installed in the wall or the ceiling
(4) 150 mm (6 in.) for recessed fluorescent luminaires installed in the wall or the ceiling
(5) Surface-mounted fluorescent or LED luminaires shall be permitted to be installed within the storage space where identified for this use.
Best Answer
There are some requirements for mains voltage lamps in a closet NEC 410.goes over these requirements. The advantage to These low voltage Low wattage lamps is the instructions allow them to be surface mounted without conduit. The transformer or supply can be used as a plug in or box mounted there is a switch in the model you listed. Code allows and even requires you to follow the manufacturers instructions so in that case where it may not be allowed with mains lighting it is possible when the instructions are followed. So is one way easier?
Yes a simple system like you have can be run on the surface without conduit. Mains voltage requires boxes for splices these handy low voltage connections do not require boxes even if you run them inside the walls. I use low voltage rings for data and cable all the time a WBF-1 low voltage box eliminator provides a mounting surface for a low voltage Jack or plug in. When it comes down to efficiency that is based on the quality of the LED 160lumens per watt is an efficient LED but smaller lower cost may only have 110 lumens per watt and that can be the same low voltage System or standard mains voltage lamps. The advantage with low voltage is plugging in & surface mounting with just double stick tape in some brands (yours has screws).