An introduction to LED strips

Let’s take a brief adventure to the strip mall and highlight some of the things you might find there!

India LED Market

(This was a side street off of Chandni Chowk in Old Delhi where LEDs are sold)

Christmas lights, made as a series of incandescent bulbs, hit the market a long long time ago. Obviously people put them on trees around Christmas time, but folks would also use them in other projects.

And, for the record, I will absolutely not judge you for leaving your Christmas lights up all year.

One problem with the incandescent light strips is that the lights are in series, so if any single bulb failed, the strip would go out, at least until they started adding a shunt. Even worse, you couldn’t lengthen or shorten the string easily because they just arranged the voltage for the incandescent bulbs such that everything would add up to the voltage from the wall.

Rope lights came later. Presumably now you can get them made from LEDs, but the early versions were also incandescent, but more designed for permenant installation and being cut into pieces as part of the install process.

If you look through old science fiction movies and TV shows, there’s a clear point at which rope lights arrived.

Star Trek TOS didn’t have any of them.

Buck Rogers in the 25th century I think hit right when they were new and had some great rope light usage. There was an episode where they had a space disco thing and kids are dancing holding rope lights. Yeah, I’m digressing but it’s the best camp and you deserve to know about it, as someone who cares enough to read this.

Star Trek TNG, spanning from the late 80s and early 90s, didn’t have rope lights exposed… but if you look carefully especially at the HD-resolution transfers, you realize that there’s a whole pile of stuff there’s the characteristic light pattern that makes it quite obvious that someone stuffed a rope light behind a panel.

What hit the scene after rope lights? Electroluminescent lighting actually predates LEDs. The GE patents date back to 1938 and it started appearing in cars in 1960. The Apollo computers used electroluminescent displays and they ended up in all kinds of consumer electronics before someone cooked up El Wire, which turned into an absurdly huge deal starting somewhere in the late-90s to early-2000s timeframe, probably because of burners. The fun part was that it was a continuous unbroken strip of color, as if someone had made neon tubing but without all of the vacuum equimpment, glassblowing, and high-voltage transformer drama.

As best I can tell, pretty much all of the people who were once doing El-Wire have stopped using it because, while it’s still kinda cute for tourist-trap glowing sunglasses, El-Wire stuff is a huge reliability headache, it’s kinda annoying to cut and solder connectors to, the power supplies like to whine, and it’s really really dim.

The next thing to hit after El Wire was LED strips made out of discrete relatively large LEDs atop flexible PCB material. Like the rope lights, these were meant to be used as architecture lighting so they were designed to be cut up into pieces. This led to a wide variety of interesting combinations, like non-intelligent RGB strips, intelligent RGB strips, and so on.

The most recent thing to hit the market is COB strips. The actual LED is not exactly large, so if you cut up a lot of tiny little LEDs and arrange them just right, you can make something that looks like El Wire except that it’s significantly brighter.

Most of the older form factors are still around. You can still get Christmas lights and they’ve got newer ones where each of the lights is an RGB pixel. You can get fairy lights that remove a lot of the bulk of Christmas lights. Rope lights are still around, too.

These are all, at this point, fairly fungible items made by a variety of manufacturers. You aren’t guaranteed that you are going to get the same strip even if you get one from the same vendor.

Using the metric system is no feet at all

Literally everything with LED strips is done with metric so everything gets very much simpler if you just use metric.

Cutting points and natural joins in an LED strip

LED strip join

LED strips are designed for ease of install. This means that they don’t require extra driver circuitry, just a power source at the correct voltage.

LED strips tend to be manufactured out of a series of continuous segments, generally about 0.5 M. Thus, you will tend to find a soldered joint connector in the middle of a 1 M strip.

LED strips tend to end up coming on a spool, usually something like 5 M. So that’s the maximum single-spool size you’d encounter.

The strip will also tend to have a line on it designating where you can cut it to break the strip in two, where there’s a pad to solder wires to on each side of the line. This is usually per-LED on most larger-sized intelligent LEDs but a lot of the non-intelligent LED strips are going to have a few LEDs in series and then some sort of resistor or driver chip, so you might be a lot more constrained about where you can cut.

Connectors

JST SM connectors

For whatever reason, LED strips and El Wire strips have all tended towards using JST-SM connectors. They do handle a reasonable amount of power, are polarized, and have a locking assembly so they can’t come loose easily.

JST-SM connectors are wire-to-wire connectors, so you’ll never find a JST-SM connector you can solder to a circuit board.

JST makes a ton of connectors in different sizes, so you really can’t say “JST connector” and expect to get the right connection. Plus, there’s a whole pile of compatible connectors made by other people in various degrees of quality.

Everybody sets up their connectors differently, so you always need to check your strips before you hook them up and probably re-wire them. You also should be careful because a 4-pin JST-SM connector for an APA102 strip also looks like the 4-pin JST-SM connector for an non-intelligent RGB strip.

There are solder-less conectors that you can squeeze on to the end of a strip, but I don’t necessarily trust them for stuff that might move.

COB strips vs. fake neon strips vs. circuit board strips

LED strip assortment

Circuit board strips are, more or less, the old standard. These are going to produce visible lit-up dots that require a diffuser, potentially a fairly heavy diffuser, to look like a single light source.

You can find fake neon strips, which are pretty much some version of the circuit board strip but where it’s encased in some sort of silicone-ish material. Someone presumably has thought through exactly how much diffuser is required, so these look pretty much like neon. Except for the part where neon is made from glass and is rigid, of course. You can also get the tubing separate from the strips, although you need to be careful because this can turn into a giant headache if they don’t quite fit.

A lot of people really love COB strips. These are much much more flexible than the fake neon strips because they don’t require nearly the degree of silicone to get a visually continuous line. Obviously, if you want to make something that still looks like a piece of neon, you’d end up encasing it in more silicone.

Another interesting new development is narrow COB strips. Wide COB strips are already magical, but the 2.7mm wide strips look magical when you wrap them around 3mm thick laser-cut acrylic.

Resisting the voltage sag

If you just connect at one end of the strip and string along a few meters, you will discover that the LEDs will dim to nothingness, frequently changing color as they fade. This is because of voltage sag.

An LED strip is basically a flexible insulator with copper plated on top. In order to be flexible, it’s not an especially thick layer of copper. Some strips that a cosplayer friend measured while we were debugging them showed between 0.5-1 ohms of resistance over a one meter length.

That doesn’t seem that bad until you plug it into the Ohm’s Law equation: Vdrop = I × R where I is the current and R is the resistance. It’s not uncommon for a strip to draw an amp or two when it’s fully on, so we’re talking about enough voltage drop to dim the LEDs at the end of the strip after a meter or two if you have a dense strip running at 5V.

On the other hand, even 22 gauge copper breadboard wire is going to be 0.053 ohms per meter. 18 gauge is 0.021 ohms per meter. Ergo, it helps to connect power every meter of strip or so. All of these strips are designed with current limiting built in, so it’s totally OK to parallel them.

When you are dealing with long strips, you probably already have some natural joins in the strips even if you find one that’s 5m continuous length, it’s just practice to run multiple power wires to different point along the strips when you are using long strips. At the very least, powering both ends, potentially adding some wires to the middle at the natural joins.

Do I want 5V or 12V or 24V? The answer might revolt you!

If you are powering two different LED strips that are the same overall brightness and wattage, one a 5V and the other one a 10V, the 10V strip will have fewer amps flowing through it. This means that the voltage drop will be lower.

Let’s look at the equations of electricity:

First, watt’s law: W = V × A, where V is the voltage and A is the amperage. Lights are converting watts of power to watts of illumination, so two lights at the same wattage and efficency are going to put out the same amount of light.

Thus, 10W strip that runs at 10V will need 1 amp of power, whereas a 10W strip that runs at 5V will need 2 amps of power.

But let’s look at the voltage drop from above, Vdrop = I × R.

If the resistance of the strip is 1 ohm, this means that the voltage drop for the strip at the end is going to be 1V (1A × 1 ohm = 1V), so the LED at the other end will see 9V instead of 10V.

On the other hand, the other strip is going to have a voltage drop of 2V (2A × 1 ohm = 2V) which means that the voltage drop is 2 volts and so the LED at the other end is going to see 3V instead of 5V.

The 10V strip is going to be dim on one end. The 5V strip might not even light up at the end.

I picked numbers for math simplicity, but you get the idea. For short strips and short wire runs, low voltage is fine but if you are running a long strip, higher voltage is great. You can sometimes get away with powering a long piece of 24v LED strip at one end, but at 5v you are going to need a lot of mid-strip power connections.

Aluminum channels and stickies and brackets and tubing

Because pretty much all popular LED light strips are a flat strip of a small number of sizes, you can get ready-made aluminum channels with diffusers on the front suitable for mounting, potentially even with corner-brackets.

You can also get strips of the silicone tubing to make neon strips out of, if you look hard enough, or you can get a strip someone has manufactured for you.

Some LED strips will come with two-sided tape on the back, although it’s not the greatest.

There are also brackets for nailing down bare LED strips easily.

There’s a whole world of LED strip products out there, so it might help to look for options.

LED strips are really really neat

India loves LED strips in ways that the US can never top. They were everywhere I went and I think they lack America’s boomer cultural baggage about colored lighting over there.

The important thing to understand about LED strips is that they are both brilliantly bright and extremely malleable. They are quite efficient. And they are the sort of thing that doesn’t require a deep understanding of electronics or even especially detailed electrician’s skills to install a bunch of.

Where to go from here?

  • Non-Intelligent LED strips
  • Intelligent LED strips
  • Perceptual illusions of brightness

Posted:

Updated: