LED Lights

From Wayne's Dusty Box of Words

Reasonably priced LED light bulbs have been around for a few years now. At this point, there's no reason to have an incandescent light bulb anywhere except in some niche product that takes a form factor for which an LED replacement hasn't yet been made. I thought I would explore just what we have here since lights are a utility function you don't think about unless they don't work.

My interest in non-incandescent light bulbs started in my woodshop oddly enough. It's in the basement like many hobbyist shops and therefore depends on artificial lighting. I do have a window, but due to its position it's only an effective light source in the late afternoon and it provides a clear view into the shop to anyone walking or driving by. Something Scott calls a "steal my shit" window. So, there are curtains that are rarely opened. So, the lights.

When I first set up shop here 20 years ago, there were two options: incandescent light bulbs and fluorescent tubes. I dislike fluorescent tubes for several reasons: they have large, fragile bulbs, they emit a low hum and they flicker at 60 Hz. They also take a while to "warm-up" to full intensity. Something especially noticeable in the winter when the shop is cool.

I chose to install two tracks for track lighting with 4 fixtures each and use 90W PAR38 floodlights. These lights are made to be used outside so they are fairly rugged and much safer to use in a shop environment than the thin-skinned typical light bulb. Plus, the track light system gave me the flexibility to aim light where needed.

But they do have a few drawbacks: color and heat.

At that time, it was hard to tell that there was a color problem because all the light bulbs in your house were incandescent. The color of the lights was… that color. But they have a "warmer" glow than sunlight or even fluorescent lights.

What does that mean for woodworking? Well, imagine that you are starting with reddish wood like pine and oak and viewing them in a "warm" light. It's hard to tell true colors in that light and any pictures you take will come out very red. It's particularly a problem when it comes to finishing where a specific color matters.

So, what do we mean by "warm" light? That sounds a little too vague. And you're right, so let's get technical. The color of light is described as a temperature in degrees Kelvin.

To understand why we need to take a little trip back to high school physics.

The color of radiation emitted from an ideal black body is defined as its surface temperature in kelvins. There's some exciting physics going on that statement, but I won't bore you. The important thing to take away is that all black body radiators at the same temperature have the same color. Therefore we can use their temperature as a shorthand to describe their spectra.

What's an example of an ideal black body radiator you ask? The Sun. All-stars with the same surface temperature as the Sun have the same color (ignoring doppler shifts), about 5900K. Of course, we are happily at the bottom of a nice atmosphere, so to us, it's about 5500K.

This is what we call "white" light.

Does that mean that get a true white light we need something heated to 5500K (9440F)? No, because…physics. Instead, we can feed 120V AC through a tungsten filament that's in a rarified atmosphere (say, argon) and it will glow at about 2700K but only give off 37W of heat (for a 40W bulb).

Back to sunlight.

Given that the color of sunlight is 5500K and we call this "white light", anything "cooler" than that will have a reddish tint and anything "warmer" will have a bluish tint.

Yes, that's counter-intuitive, cooler lights appear "warmer" to us. As I mentioned incandescent bulbs shine at about 2700K. Marketing on light bulb boxes now calls this "warm white".

Fluorescent bulbs vary depending on the gas they use, but the CFL bulbs you might have in your home shine at about 3500K. That's better than it sounds since the color scale isn't linear. But still not great.

Then we get to the heat. Incandescent bulbs are about 5% efficient. So my track lighting system is producing 684W (8 x 90 x .95) of waste heat along with the 11,500 lumens of light. That doesn't seem like a lot, but over the course of an hour or three, especially in a small shop in the summer and it's downright toasty.

So when compact fluorescents came out, I jumped on them as replacements. First of all, they only used 13W of power versus 90W. But, they are also more efficient and my 8 little space heaters were down to a manageable total waste heat of 40W or so. Quite a difference.

But they sucked. They took minutes to come up to full brightness and that level of brightness was not nearly as bright as the incandescent bulbs were. I ended up adding several more fixtures to make up for the losses and still had a 300W halogen task light over my workbench for fine work.

Meh.

So the new problem is output. This is measured in lumens. Most retail packaging assumes you are too stupid to know what that is, so they omit it. As a bonus, it also makes it hard for you to comparison shop one brand to another.

The output of a light bulb is completely described by its color temperature (K) and its output (lm). That's all you need to know to compare one bulb to another. Though, you could also consider power consumed (in watts) if you are pinching pennies.

So what are lumens and what's a "good" number?

A typical (if you can still find one) incandescent light bulb has a luminous efficacy of 16 lumens/watt or about 960 lm for a 60W bulb. My original shop lights produced about 1440 lm each for a total of 11,500 lm.

The luminous efficacy of CFL bulbs is about 50-70 lm/W. The bulbs available at the time were 13W bulbs. So my heat farm went from 720W giving 11,500 lumens @ 2700K to 104W giving 5000-7000 lumens @ 3500K. Dramatic savings in energy (and waste heat), but only half the light. And it's worse than that.

Back to physics. Fluorescent lights operate by exciting mercury atoms in the tube which emits UV light (which we can't see) but is converted to visible light when it strikes the phosphor coating in the inside of the tube.

What does this mean? The entire surface of the tube glows, including the inside of the little twisty element, making for more diffuse light. In incandescent bulbs, the whole filament glows, but it's such a compact area that you can fit a very nice reflector in the back of the bulb. CFL bulbs are much bigger and there's no room for a reflector.

I went through at least 2 generations of CFL bulbs as they got better (color-wise) and came out in high power. But they were dim, the color was bad and took forever to come up to full brightness especially in the winter when I need them most.

Then along came LEDs.

The quest to develop white light LED took decades of research before scientists hit upon the right combination of materials to produce an efficient white light LED. They became commercially available about 5 years ago and have quickly supplanted the CFL bulb.

LEDs have a ton of advantages. They are rugged, they can be produced in nearly any color, they have a far higher luminous efficacy, they use even less energy than CFL and (in theory) last effectively forever as they are quoting 10,000 to 50,000 hour light spans (more on that in a minute).

Back to the workshop. I now have 5 tracks holding a total of 20 fixtures. Some making up for the CFL shortfall, some because I need more light these days, not sure why. My current bulbs are 11W and 13W and the luminous efficacy of the current generation is around 200 lm/W (there are 300+ lm/W in the pipeline). So, I am burning 240W of electricity to get a whopping 48,000 lm of light at 5000K. I think we have arrived.

I have a work environment with almost no shadows, that's daylight balanced and doesn't turn the shop into a sauna. I'm happy. I have installed a rollup backdrop so I can shoot my work right there on the bench as I finish it.

Now, there are a few issues, of course.

First, life expectancy. Manufacturers claim a life as long as 50,000 hours. To put that into human terms, if you use the light 6 hr/day, every day, it would last 22.83 years. Forever. But I have already replaced as many of my new 13W daylight-balanced LED lights as I did the 90W incandescent floods (rated at 1,000 to 2,000 hours) I started within the 3-4 years I had them, 1. Why?

There could be a couple of reasons most of them related to cheap manufacturing processes. To understand the possibilities, we need to look at how these light bulbs do what they do.

The screw-in replacement bulb has 3 main parts: power supply, support electronics and the LED itself. All wrapped into an incandescent bulb-shaped package. Each of these as the potential to fail in different ways.

The LED is, as the name implies, a diode. The main feature of a diode is that the current will only flow in the forward direction. No current flows and no light is emitted if the voltage is applied in the reverse direction. And, if the reverse voltage exceeds the breakdown voltage, the LED will be destroyed. This isn't a concern in a light fixture. So we can ignore this vulnerability.

Another characteristic of diodes is that the current rises exponentially with the applied voltage, so a small change in voltage can cause a large change in current. While you might think this isn't an issue either, you'd be wrong.

You are probably aware of occasions when "the lights dimmed" or flickered. Either by a sudden load within your house or as the result of a storm. While that wall outlet provides a nominal 110v, and that's usually pretty close, it can sag or surge as much as 10% or 20%.

For LEDs, a sag wouldn't be a problem, but a 20% surge would probably kill your lights.

LEDs operate on 5-10v DC. Therefore, all of these replacement fixtures include a power converter built into the base that changes 110VAC to 5VDC. In theory, these power supplies would be constant-voltage sources with, at least, a current limiting resistor. But… we want these things cheap and small, right?

I disassembled the first one I had that failed to see what's really in there. Surprisingly little was what I found. In the base was a very small circuit board holding two transformers for stepping down the voltage and a couple of capacitors and an integrated circuit, one or two other things. This was wired to the actual LED chip that sat in a reflector at the back of the bulb area.

Over the years I've built and repaired quite a few computers. One of the most common failures I have seen is in the power supplies where the main current leveling capacitors blew (literally). Computer parts have become such commodity items that every possible corner that can be cut has been cut and then some. I stopped using "house brand" power supplies after the 3rd one failed on me. Now I buy a premium brand that uses more robust parts and is more efficient. It costs 3 times as much, but I don't feel like I need to keep a spare on hand at all times either.

I have had to replace 3 or 4 LED light bulbs and they all showed the same symptoms before failure: either flickering or intermittent on/off. This leads me to suspect this power supply crapping out. To explain why that makes sense would require a side trip into the function of switching power supplies which is something you don't want to know, and this article is way too long already.

The bottom line is that no matter what the lifespan of the LED itself might be, current commercial packages marry them to garbage power supplies that simply won't last anywhere near as long as the LED.

Finally, there is heat. I don't recommend using them in an enclosed fixture. The LED ship itself generates considerable heat for its size and lacks the large radiative surface of the incandescent and fluorescent bulbs. The danger isn't fire, it's that the trapped heat will hasten the demise of the aforementioned crappy power supply.

If you must use an enclosed fixture, say a porch light, use one that has vents or has a large metal heat sink around the lower portion of the bulb. Of course, they cost more, but you won't have to replace them.