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 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 wood shop, oddly enough. Like many hobbyist shops, it’s in the basement and depends on artificial lighting. I do have a window, but due to its position, it’s only a good 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. The curtains I have on that window to keep prying eyes at bay spend most of their time drawn. It’s hard to reach over the workbench to pull them, so I rarely bother.
When I first set up shop here 20 years ago, there were two options: incandescent light bulbs and fluorescent tubes. I’m not too fond of 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, especially in the winter when the shop is cool.
I chose to install two tracks for track lighting with four fixtures each and use 90W PAR38 floodlights. They made these for outdoor use, so they are pretty 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. So 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. We describe the color of light 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 in that statement, but I won’t bore you. The critical 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. Ignoring changes caused by Doppler shifts, any star with the same surface temperature as the Sun have the same color, about 5900K. Of course, we are happily at the bottom of a thick atmosphere, so to us, it’s about 5500K.
Therefore, 5500K is the “white” light’s temperature (color).
Does that mean that we need something heated to 5500K (9440F) to get a true white light? No, because…physics. Instead, we can feed 120V AC through a tungsten filament in a rarified atmosphere (say, argon), and it will glow at about 2700K but only give off 37W of heat (for a 40W bulb).
Let’s go 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. See the drawing to the right.
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 for an hour or three, especially in a small shop in the summer, and it’s downright toasty.
So when compact fluorescent bulbs 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 eight little space heaters were down to a manageable total waste heat of 40W or so—quite a difference.
But they sucked. The CFLs took minutes to come up to full brightness, and that brightness level was not nearly as bright as the incandescent bulbs were. So 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. We measure the intensity or output of a light bulb 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 any light bulb can be entirely described by its color temperature (K) and its output (lm). That’s all you need to know to compare one bulb to another. Of course, 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 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 two generations of CFL bulbs as they got better (color-wise) and came out in high power. But they were dim; the color was terrible 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 five years ago and have quickly supplanted the CFL bulb.
LEDs have a ton of advantages. They are rugged, can be produced in nearly any color, have a far higher luminous efficacy, and use even less energy than CFL. In addition, they should last effectively forever, given the quoted life span of between 10,000 and 50,000 hours (more on that in a minute).
Let’s head back to the workshop. I now have five tracks holding a total of 20 fixtures. Some are 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 is daylight balanced and don’t turn the shop into a sauna. I’m happy. I have installed a rollup backdrop to shoot my work right there on the bench as I finish it.
Now, there are a few issues, of course.
First, let’s talk about 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 will 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. Why?
There could be a couple of reasons, most of them related to cheap manufacturing processes. First, however, we need to look at how these light bulbs work to understand the possibilities.
The screw-in replacement bulb has three main parts: power supply, support electronics, and LED. All wrapped into an incandescent bulb-shaped package. Each of these has the potential to fail in different ways.
The LED is, as the name implies, a diode. The main feature is that the current will only flow in the forward direction. So if we apply voltage in the reverse direction, no current flows, and the LED emits no light. And, if the reverse voltage exceeds the breakdown voltage, you will destroy the LED. However, a reverse voltage 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 slight change in voltage can cause a significant difference 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%.
A sag wouldn’t be a problem for LEDs, but a 20% surge would probably kill your lights.
LEDs operate on 5-10v DC. Therefore, 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 was really in there. Surprisingly little was what I found. A tiny circuit board held two transformers for stepping down the voltage, a couple of capacitors, an integrated circuit, and a couple of other components in the base. This circuit board also connected 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 the power supplies where the main current leveling capacitors blew (literally). Computer parts have become such commodity items that most manufacturers have cut every possible corner and then some. I stopped using “house brand” power supplies after the 3rd one failed me. Now I buy a premium brand that uses more robust parts and is more efficient. It costs three 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. That behavior leads me to suspect this power supply is crapping out. To explain why that makes sense would require a side trip into 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 won’t last anywhere near as long as the LED.
Finally, there is heat. I don’t recommend using LEDs in an enclosed fixture. The LED ship itself generates considerable heat for its size and lacks the sizeable 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.