So you want to use LED lights...

Submitted by Andrea on March 23, 2012
Addendum: We got more advice and decided to wait on installing LED strip lights. Read more in "Stepping back temporarily from LEDs" (May 9, 2012).

I could not have designed and built this house without our good friend Google. I created all of the 3-D drawings in the free version of SketchUp, and I researched literally every component of this house using Google's indispensable search engine.

Unfortunately Google is nearly useless for researching items that are aggressively marketed online, particularly LED lights. The problem is that discount LED vendors use every trick in the book to rank among the top Google search results, so it's nearly impossible to find helpful online advice about how to buy LED strip lights.

Until recently I had only a dim (ha!) idea of what components we'd need for LED strip lighting. But now that we've figured it all out and completed our lighting schedule, I'd like to share what I've learned about illuminating a room primarily with LEDs.

Not all LED lights are created equal

I do not usually use all-caps (the Internet equivalent of screaming), but this is hugely important. It is tempting to order LEDs online from discount vendors, and you might know people who like the lights they purchased that way. Ted and I have some friends in Austin who purchased a lot of accent lighting from Eco Light LED, and the lights look really cool. Installed inside bookcases and behind valances, they have RGB controllers and can be adjusted to display a huge range of fun colors. Ted and I assumed we'd light our house with something similar, only on a larger scale.

We subsequently learned, however, that you can only get away with cheap LEDs if you aren't using them as a primary lighting source. When you look at a person, you're seeing the light that's bouncing off of them; the surface of their clothing, skin, etc., absorbs certain parts of the spectrum and reflects the rest back out. So if your light source is missing crucial colors, that person will look downright creepy.

Any decent LED manufacturer will publish the product's Color Rendering Index (CRI). This is an adequate (though incomplete) measure of the light's color fidelity. CRI is measured on a scale from 1-100, with ordinary incandescent lights at 100 and everything else somewhere below that. For your primary indoor lighting source, you shouldn't go below a CRI of 80.

Color temperature is also important, and it is easily misunderstood. "Warm" light actually has a lower temperature — incandescent bulbs are 2,700K and those blue-white LED xmas lights are around 6,000K (compact fluorescent bulbs usually range from 2,700 to 3,500K). All of our LED lights will have a color temperature around 3,000K and a CRI in the mid-80s.

Once you know a little about CRI and color temperature, the discount LED vendors no longer look so good. Eco Light sells Warm White LED Strip Lights for about one-quarter the price of the strip lights we're buying, but a closer look at their downloadable spec sheet reveals that the color temp is a not-so-warm 3,500K, and they don't mention CRI at all. I found CRI info on a few other discount sites, but the numbers were unacceptably low (70-75).

Most of our LED strips will be installed behind a valance, with the light shining upwards across the ceiling (the sole exception is the under-cabinet lights in the kitchen). The LEDs we selected have a good overall CRI (85) but are a little weak in the red part of the spectrum, which means we need to choose ceiling paint with a hint of red pigment so it won't absorb all the red coming from the LEDs. Our lighting consultant told us a cautionary tale about how indirect non-incandescent light bouncing off cream-colored walls can turn everything yellow, and we don't want that to happen to us. In fact, we had planned on using pigmented plaster for our walls, rather than the usual paint over drywall, but the lack of fine-grained color control pushed us back to the standard approach.

LED strip lighting basics

The first thing to know about LED strip lights is that they run at a much lower voltage than most other electric devices in your house. In North America, we use 120 volts AC (alternating current), and most LED strip lights run at either 12 or 24 volts DC (direct current). You will therefore need a transformer to convert from line voltage (120V) to the voltage of your LED system.

In case you're rusty on how electricity works, I should point out that the voltage has nothing to do with how much energy the lights draw. Voltage is analogous to water pressure (not the total amount of energy used), so the important number is how many watts a fixture requires.

Each circuit of strip lighting will require its own transformer (by "circuit" I mean a strip that's controlled by its own switch), and the total wattage of the strip lights cannot exceed the maximum output of the transformer. Our strip lighting draws 3W per foot and our longest stretch on a single circuit is 14'-4" (the upstairs hallway), which means our heaviest circuit will only draw 43W. The smaller WAC Lighting transformer is rated up to 60W, so we'll be well within the limit.

In case you're curious, here's what you'd need to run 14'-4" of strip lighting:

  • Two 2-inch LED strip lights
  • Four 1-foot LED strip lights
  • Two 5-foot LED strip lights
  • One 12-foot lead wire (connects the light strips to the remote transformer)
  • One end cap
  • One remote transformer (driver). Converts from 120V (line voltage) to the 24V required by the lights.
  • One dimmer switch for an electronic low-voltage fixture

Each segment of strip lights connects to the next, and the end cap terminates the string.

Incidentally, the reason we're fiddling with the 2-inch segments instead of just trimming a 1-foot segment (the lights are trimmable every three inches) is that it's marginally less expensive. This will give us the exact length we need.

Why bother with LEDs?

I confess that writing this post has made me wonder why we're installing LED strips when CFLs use roughly the same amount of power. People criticize fluorescent bulbs (compact and otherwise) for containing mercury, but it's just a tiny amount and can be recovered if the bulb is properly recycled. LEDs don't contain mercury, but various toxic chemicals are used during production, and their heat sinks are made from valuable metals like aluminum.

So why are we using LEDs? I suppose it's partly the eco-bling factor. But we're installing plenty of conventional fixtures too, and in the short run we'll probably fit most of them with CFLs. LED replacement bulbs tend to shine in a single direction; this makes them a good choice for recessed downlights, but not so good for wall sconces and multidirectional fixtures.

We considered using a series of T5 fluorescent tubes for all the indirect lighting, but then we'd run into "socket gap" — dark spots where two bulbs meet. We would also have to build a larger valance to hide the bulbs, and there are a few places where we need to keep the valance quite small.

We therefore succumbed to the blingy lure of LEDs, and I sincerely hope they'll earn their keep during their projected 50,000-hour lifespan. That's 17 years, assuming we run them eight hours a day, which I doubt we'll do. Again, this is why it's important to choose the manufacturer carefully, since we're likely to be stuck with these things for a long long time.

I keep thinking I can cover lighting in a single post, but each time I try I wind up having too much to say. In a future post I'll share diagrams and photos of our indirect lighting setups. I'd also like to talk a little about switches (whee!), and now that my eyes have been opened to the subtle art of lighting design you can expect a rant or two about bad lighting.

Added on May 9, 2012: We changed our minds. See "Stepping back temporarily from LEDs" for the details.