Low voltage LED lighting

[Don Y]

Hi,

We're looking into installing low voltage, under cabinet
lighting in the kitchen. I assume these are driven with
a (variable) constant current source? Or, PWM?

Regardless, I plan on locating a switched outlet atop
the cabinetry to power the "power source". Then, some
conductors down behind the cabinets terminating at
the underside for attachment to the LED strips.

I believe many of these power sources have support
for an intensity control. I would like to locate that
somewhere invisible, yet accessible -- most likely
alongside the LED strips on the cabinet undersides.

(we don't envision changing this often, once we've determined
the appropriate intensity level for our needs)

I assume this is just a pot? Is it operating at a low
voltage? (i.e., what Code ramifications pertain?)
Would a small gauge wire pair -- possibly in a shield -- be
sufficient?

Lastly, pointers to suitable products? (power + LEDs)

Thanks!
--don

 

[Kaz Kylheku]

Hi,

We're looking into installing low voltage, under cabinet
lighting in the kitchen.

www.homedepot.com

(Not an endorsement.)

 

[PeterD]

www.homedepot.com

(Not an endorsement.)

HD's products are a tad expensive. And though some are dimmable, they
may not meet the OP's needs.

I have a similar issue I'm working on, in my case I want to connect the
new under cabinet LEDs to an existing dimmable light in the oven hood,
so they go on at the same time. Since the oven hood has a dimmer already
I need something that will work with it.

 

[SMS]

Hi,

We're looking into installing low voltage, under cabinet
lighting in the kitchen. I assume these are driven with
a (variable) constant current source? Or, PWM?

The ones I've seen operate from a 12VDC source and current limiting is
built into the strip. Intensity controls are probably just a high
wattage pot or a variable voltage regulator:

<http://www.ledlightsworld.com/12v-inline-led-dimmer-switch-with-rotary-knob-2a-24w-p-191.html>

If you want to adjust the intensity you could try using a variable
voltage regulator to drop the 12V down. Just be sure to consider the
amount of current drawn by a large number of LEDs.

You might want to look here: <http://www.ledlightsworld.com/>. Some of
their kits come with dimmers.

Also see
<http://www.dealextreme.com/p/led-single-color-dimmer-with-remote-controller-dc-12v-82778>.
They also sell a lot of LED strips.

 

[Don Y]

Hi Kaz,

www.homedepot.com

(Not an endorsement.)

If you've spoken about anything "technical" with the HD staff
(or Lowes, for that matter), you'd realize that they aren't
very knowledgeable, at all. Surely not enough to answer the
questions I raised in my post!

I've also learned not to trust their "experts" when it comes
to plumbing, fire or electric codes -- something that, presumably,
they have expertise in!

 

[Don Y]

Hi Peter,

HD's products are a tad expensive. And though some are dimmable, they
may not meet the OP's needs.

I'm looking for answers more than products. I.e., I want to run
the wire before putting up the wallboard. Thereafter, *changing*
the type of wire used gets to be a PITA.

I have a similar issue I'm working on, in my case I want to connect the
new under cabinet LEDs to an existing dimmable light in the oven hood,
so they go on at the same time. Since the oven hood has a dimmer already
I need something that will work with it.

Are you wanting the light to simply "go on"? Or, to (roughly)
track the intensity of the *dimmed* light?

 

[Don Y]

On 9/21/2011 9:39 PM, Don Y wrote:

The ones I've seen operate from a 12VDC source and current limiting is
built into the strip. Intensity controls are probably just a high
wattage pot or a variable voltage regulator:

<http://www.ledlightsworld.com/12v-inline-led-dimmer-switch-with-rotary-knob-2a-24w-p-191.html>

In that case, I would suspect a PWM controller. Silly to use an
"energy efficient" light source with a controller that just turns
unneeded power into heat!

If you want to adjust the intensity you could try using a variable
voltage regulator to drop the 12V down. Just be sure to consider the
amount of current drawn by a large number of LEDs.

You might want to look here: <http://www.ledlightsworld.com/>. Some of
their kits come with dimmers.

A lot of the dimmers I have seen are either *on* the controller
(which is impractical as ours will be located up at the ceiling)
*or* RF (?) "remotes" -- which seems just silly.

I'd prefer a "knob" colocated with the lamps that I could just
reach up (knowing where it was located without even having to
look under the counter) and twist, as required.

The issue, then, is connecting that know to that controller!

Also see
<http://www.dealextreme.com/p/led-single-color-dimmer-with-remote-controller-dc-12v-82778>.
They also sell a lot of LED strips.

I'd be wary of DX in this case. It seems like heatsinking is the
important issue, here. I can just imagine them selling strips
of LEDs with *nothing* to address the thermal issues ("Why are
my LED lights fading?"). Since airflow is already hindered in
this sort of application, I'd want some assurances that the
vendor at least *tried* to address it!

 

[Ecnerwal]

I'm looking for answers more than products. I.e., I want to run
the wire before putting up the wallboard. Thereafter, *changing*
the type of wire used gets to be a PITA.

Conduit. Then whatever wire you need, later, you can run, later, with no
fuss and no need to figure it out when you are still putting wallboard
on. Useful stuff, especially since you appear to be heading for having
to roll your own system in order to get what you want.

and in a different post:

Silly to use an "energy efficient" light source with a controller
that just turns unneeded power into heat!

Plenty of buyers that won't even notice that their LED lights are
inefficient, so long as it says "LED" on the package and they are sure
that means it's efficient, or new, or what's in the design magazines, or
what the Jones's they are trying keep up with got last week. If there
isn't a "Lumens per watt" figure easily findable, you can bet it isn't
too good. Some customers may be like Ed, and don't want it to be
efficient, so they can maintain the dream of setting each LED "just so"
by altering its individual resistor. But most customers are just
ignorant, and cheap LED lights are cheap first, efficient only by
accident if at all. Cheap often does not mean inexpensive, either, at
least at the consumer end of the chain.

 

[[email protected]]

Hi Kaz,



If you've spoken about anything "technical" with the HD staff
(or Lowes, for that matter), you'd realize that they aren't
very knowledgeable, at all. Surely not enough to answer the
questions I raised in my post!

That certainly depends on the individuals (and sometimes stores) involved.
I've found some very knowledgeable people in these places. Some are retired
contractors, some are between jobs.

I've also learned not to trust their "experts" when it comes
to plumbing, fire or electric codes -- something that, presumably,
they have expertise in!

So you "just do it"?

 

[Don Y]

That certainly depends on the individuals (and sometimes stores) involved.
I've found some very knowledgeable people in these places. Some are retired
contractors, some are between jobs.


So you "just do it"?

No, I find *truly* knowledgeable people:

Q: "Can I run an outlet for our electric kiln off the same feed
for the electric stove? It has a comparable ampacity and I
will never use both at the same time."
HD: "Sure -- as long as you don't have both on at the same time
(which would exceed the ampacity of the circuit)"
A: "No. A dedicated circuit is required for the stove, regardless
of that circuit's ampacity. Furthermore, a circuit for the
kiln would require GFCI protection (outdoors) -- something not
present on a circuit for a stove."

Q: "How do I install this drop-in range?"
HD: "Build a base out of 2x4's to support the stove..."
A: "Do NOT build a base. The stove is supported from above -- by
the adjoining countertops."

Q: "Can I put these devices and conductors in a J-box of this size?"
HD: "Sure! Just be sure to push them in all the way so they don't
interfere with the outlets/switches/etc. you are installing."
A: "No. You will need 2 volume units for each device, 1 for each
conductor entering or passing through the box plus another to be
shared by all of the grounds. Since the sizes of the conductors
vary, you will use the volume unit associated with the largest
conductor. If you 'do the math', you'll see that you're shy by
a few cu in -- and that makes no allowances for the oversized
wirenuts you'll be needing for that many conductors. That's
why the Code goes to such lengths to explain how to size a
box properly!"

Q: "How much larger should the RO for this window be than the
window itself?"
HD: "Half an inch on each axis"
A: "A *quarter* inch on each axis -- unless you are a klutz at
framing (in which case, why are *you* trying to do this?)!
Otherwise, you run the risk of the nailing fin not having
any 'meat' to fasten onto."

Q: "Do you sell backer rod for window installation?"
HD: "No, use this self-expanding foam, instead! It's really easy!"
A: "Do NOT use self-expanding foam. The forces it exerts are
great enough to deform the window frame. Use of that foam will
void your warranty."

Q: "What if the sill isn't level?"
HD: "Use shims to level the window as you install it."
A: "The sill *must* be level. Don't shim the underside of a
fiberglass frame of that size."

Q: "Do you sell self-adhesive flashing?"
HD: "Sure. Right over here."
A: "No, that's regular aluminum (or copper) flashing. And, you
will note that it isn't even self-adhesive! I'll go see if
Lowes carries it..."

Q: "I'm wiring the house for satellite/CATV. Should I use RG6
or RG59?"
HD: "Use RG59 for video cable."
A: "No, use RG6 for satelite/cable feeds. Use RG59 for baseband
applications (at most)."

[I won't add the episode where the kid running the saw asked me
to show him how to measure 10 inches with a tape rule!]

----

Do you *really* think they're going to be able to tell me if
the dimmer control operates on the low voltage side of the
circuit instead of the mains? Do you really think they know
what PWM is? Do you think they know what sort of impedance
the "control's" terminals look into?

If you're lucky, they'll say, "Gee, I don't know. Let's see
what it says on the box...". And, since I can read at least
as well as they can, why drag them into the mix?

 

[Don Y]

Conduit. Then whatever wire you need, later, you can run, later, with no
fuss and no need to figure it out when you are still putting wallboard
on. Useful stuff, especially since you appear to be heading for having
to roll your own system in order to get what you want.

Hmmm... good idea. But, that would make for a *lot* of work!
I'd have to go through 3 ceiling joists (think about the logistics,
there... EMT is *rigid* so you can't just snake it through a
series of colinear holes in the joists!) and then down into the
wall.

and in a different post:

Plenty of buyers that won't even notice that their LED lights are
inefficient, so long as it says "LED" on the package and they are sure
that means it's efficient, or new, or what's in the design magazines, or
what the Jones's they are trying keep up with got last week. If there
isn't a "Lumens per watt" figure easily findable, you can bet it isn't
too good. Some customers may be like Ed, and don't want it to be
efficient, so they can maintain the dream of setting each LED "just so"
by altering its individual resistor. But most customers are just
ignorant, and cheap LED lights are cheap first, efficient only by
accident if at all. Cheap often does not mean inexpensive, either, at
least at the consumer end of the chain.

We're more concerned with getting lots of light with little heat.
And, in a very low profile form factor (don't want to have to
build a light shield or add unnecessary trim to hide a bulky
fixture under the cabinetry).

I tried playing with some A-base incandescent replacements
(1x1W, 3x1W, 5x1W, 7x1W, etc.) LED lamps but they must have
something inside that effectively makes them nonlinear devices.
E.g., on a "standard dimmer", there was *no* difference in
light output over the entire dimmer range!

[note these weren't intended to be used in the under-cabinet
application... more a curiosity factor. Didn't like the color
of the lamps, either, esp when it came to use in a kitchen!
"Is this meat *raw*? Or, does the light just make it look
that way??"]

 

[Ecnerwal]

Hmmm... good idea. But, that would make for a *lot* of work!
I'd have to go through 3 ceiling joists (think about the logistics,
there... EMT is *rigid* so you can't just snake it through a
series of colinear holes in the joists!) and then down into the
wall.

I didn't specify EMT - there are many types of conduit. You use what
works best for each situation. If you're sure it's going to be low
voltage, there's the orange flexi-hose stuff. If not, there are flexible
types that are suitable for line voltage applications. PVC and glue are
sometimes the best approach. EMT is not really rigid, either - rigid is
rigid, EMT is somewhat easily bent. If you simply had to have EMT, a few
couplings on short sections of EMT would get you through your joists, if
there isn't a place (or it's done at the wrong time) to feed it into the
joists in one piece. Far from insurmountable, and no more than work -
not a *lot* of work, just work.

We're more concerned with getting lots of light with little heat.
And, in a very low profile form factor (don't want to have to
build a light shield or add unnecessary trim to hide a bulky
fixture under the cabinetry).

Always good to hit the core of the problem. LEDs may well be your best
bet, but you might also look at cold cathode lamps - small diameter
"neon" or "fluorescent" type lamps sold mostly in the "case modding" (PC
gamer systems) community. I'm not a case-modding PC gamer, but they do
make nice 12V lighting available at the sort of prices that volume
production enables. I got some whites, and also red/blue/green tubes to
play with a few years back. They have a small inverter which runs the
12V up to 600V or so to light the tubes.

There are also low-profile 120VAC T4 & T5 fluorescent fixtures, some of
which are small enough to conceal at the front of a typical cabinet just
from the usual "lip" where the face goes below the bottom shelf of the
cabinet (if mounted with the base against the inside of the face, not up
into the bottom shelf).

Not sure about dimming being easily available with either of those,
however.

Color, (or color temperature) is highly subjective. I'm used to cool
white fluorescent in kitchens, and find all-incandescent kitchens (and
warm-white LEDs or fluorescents) odd as a result. Then again, some of
the "daylight" stuff looks too blue to me.

 

[Don Y]

I didn't specify EMT - there are many types of conduit. You use what
works best for each situation. If you're sure it's going to be low
voltage, there's the orange flexi-hose stuff. If not, there are flexible
types that are suitable for line voltage applications. PVC and glue are
sometimes the best approach. EMT is not really rigid, either - rigid is
rigid, EMT is somewhat easily bent. If you simply had to have EMT, a few
couplings on short sections of EMT would get you through your joists, if
there isn't a place (or it's done at the wrong time) to feed it into the
joists in one piece. Far from insurmountable, and no more than work -
not a *lot* of work, just work.

If all I have to run is a shielded two conductor cable, it's a lot
more work than necessary! :<

I figure if I was charged with designing a dim-able supply for LED
lighting, I would either come up with a design that could hang off
a conventional triac dimmer; or, something where the dimming *control*
(assuming the entire power supply couldn't fit in a J-box) ran at low
voltage/current -- so it could be unencumbered by code requirements.

I'm gambling that the latter is the case.

Always good to hit the core of the problem. LEDs may well be your best
bet, but you might also look at cold cathode lamps - small diameter
"neon" or "fluorescent" type lamps sold mostly in the "case modding" (PC
gamer systems) community. I'm not a case-modding PC gamer, but they do
make nice 12V lighting available at the sort of prices that volume
production enables. I got some whites, and also red/blue/green tubes to
play with a few years back. They have a small inverter which runs the
12V up to 600V or so to light the tubes.

I had thought of the CCFL's from LCD monitors -- but dismissed them
due to packaging concerns. The gamer-PC idea is an interesting angle...

But, we are really "down" on fluorescents. The light is just too
cool/blue in many cases. Some of the CFL's are tolerable color
but don't dim, etc.

We've been using 130V incandescents (last longer) for most of the
recessed lighting and find that it is just about perfect -- with
the dimmers set at absolute minimum, it gives a soft glow to
everything that is just enough light for visitors (unfamiliar
with the layout of the house) to get around "in the dark" -- yet
not bright enough to fry your eyes when waking from a sound sleep.

In the kitchen, I've found the cool lighting to make meal preparation
tedious. Too hard to gauge colors of seasonings, meat, etc.

Elsewhere, the warmth of the lights seems more natural for
viewing artwork, painting, etc.

There are also low-profile 120VAC T4& T5 fluorescent fixtures, some of
which are small enough to conceal at the front of a typical cabinet just
from the usual "lip" where the face goes below the bottom shelf of the
cabinet (if mounted with the base against the inside of the face, not up
into the bottom shelf).

Yes, we looked at that as well and decided against it. More "bulbs"
to replace, etc. We figure the LEDs will outlive *us* -- even if
we might have to replace a power supply down the line.

Not sure about dimming being easily available with either of those,
however.

Color, (or color temperature) is highly subjective. I'm used to cool
white fluorescent in kitchens, and find all-incandescent kitchens (and
warm-white LEDs or fluorescents) odd as a result. Then again, some of
the "daylight" stuff looks too blue to me.

I have cool LED lights in my office. At night, passersby can see a
noticeable difference in the light cast from that room and other
rooms as the former is very "blue" (cold) while the others considerably
warmer.

 

[Rich Grise]

We're looking into installing low voltage, under cabinet
lighting in the kitchen. I assume these are driven with
a (variable) constant current source? Or, PWM?

Why not, rather than making an ass out of u and me, go to
the place that sells them and ask?

Thanks,
Rich

 

[PeterD]

Hi Peter,


Are you wanting the light to simply "go on"? Or, to (roughly)
track the intensity of the *dimmed* light?

The current light has 'high' and 'low' settings. I'd love to get both on
the LED light, but if I got only high I'd live! I suspect a relay might
just do the trick but would rather keep it simple.

 

[Ecnerwal]

it gives a soft glow to
everything that is just enough light for visitors (unfamiliar
with the layout of the house) to get around "in the dark" -- yet
not bright enough to fry your eyes when waking from a sound sleep.

For that application I like red LEDs on a battery-backed 12V supply (as
in, you can get out of the house in the event of a power outage and a
need to get out of the house in the dark, and do so without destroying
your night vision) with far less power and heat generated.

 

[Don Y]

Hi Peter,

The current light has 'high' and 'low' settings. I'd love to get both on
the LED light, but if I got only high I'd live! I suspect a relay might
just do the trick but would rather keep it simple.

Is it, perhaps, a regular 120V lamp and the switch just supplies
power, half-wave power or *no* power (hi, lo, off)?

 

[Don Y]

For that application I like red LEDs on a battery-backed 12V supply (as
in, you can get out of the house in the event of a power outage and a
need to get out of the house in the dark, and do so without destroying
your night vision) with far less power and heat generated.

We only leave the lights on when we have house guests.
Just about all of the "public" living areas are equipped
with dimmers so the entire house can be in this "low light"
state. Helpful if, for example, you wanted to find your
way to the refrigerator for a late snack/beverage.

*Without* house guests, we can find our way without *any*
light (which every person should be able to do as fire/smoke
will deprive you of even the brightest light sources!)

 

[John S]

Why not, rather than making an ass out of u and me, go to
the place that sells them and ask?

Thanks,
Rich

They've been through that. Read the entire thread.

 

[[email protected]]

We only leave the lights on when we have house guests.
Just about all of the "public" living areas are equipped
with dimmers so the entire house can be in this "low light"
state. Helpful if, for example, you wanted to find your
way to the refrigerator for a late snack/beverage.

*Without* house guests, we can find our way without *any*
light (which every person should be able to do as fire/smoke
will deprive you of even the brightest light sources!)

Same here. However, sometimes the cat is sleeps in the middle of the back
hallway. It doesn't help that he's all black.