It used to be pretty simple to buy a light bulb.  Barring specialty items, you just went to the store and bought a “standard” light bulb.  The more watts the more light – 60 W was normal, 40 a bit dim, 100 W as bright as most sockets could handle.  Oh yeah, you had to choose clear or frosted, but that was pretty much it, right?  The common light bulb was available just about anywhere.  The standard American screw type light bulb was invented in 1909 and for about a century, not too much changed until recently.

If you go to buy a light bulb today, it can be bewildering to figure out exactly which bulb you need.  Consider this a primer on light bulbs for the average home owner.  There are literally thousands of light bulb varieties, but most of these are specialized for various applications that really don’t concern the average home owner.   As someone who is a photographer and has a degree in Physics, I am pretty familiar with much of the techno-babble surrounding this topic.  I also worked one summer in a wholesale electrical supply warehouse – but that’s another story.  I thought I would try to de mystify some of all this for the average home owner.

light-bulb-types

Technology

There are three principal technologies we are concerned with – incandescent (think “old style”), CFL (compact Fluorescent Lightbulb), and the newest, LED (Light Emitting Diode).

Incandescent bulbs work by heating up a wire until it gets so hot it emits light.  Halogen bulbs are a particular type of incandescent bulbs that use a tungsten coated wire and include halogen gases in the bulb so it can operate at higher temperatures and wattages, putting out more light.  Unfortunately most of the energy used by an incandescent light bulb is emitted as heat and only about 2% produces light in the visible spectrum.  But they are cheap – basically a little wire held inside a glass container under vacuum and presto – the light bulb.

  • Good – cheap, standardized, familiar, “the standard” for our expectations of the amount of light and the quality of light.
  • Bad – inefficient, relatively fragile, short operational life.

Flourescent and Compact Flourescent (CFL) bulbs work by exciting low pressure mercury vapor to create UV light that causes a phosphorescent coating on the bulb to fluoresce or glow.   Fluorescent light bulbs, including CFLs require an electrical component called a ballast that limits the current flow through the bulb, otherwise they would self destruct.  The ballast is build into CFL bulbs, which is a major portion of their cost, whereas typical large “shop” fluorescent fixtures have discrete external ballasts, which is why the tubes are so inexpensive.

  • Good – moderate price (has come down dramatically), more energy efficient, longer lasting, wide variety of options.
  • Bad – contain mercury vapor (dispose of properly!), poor quality of light (see below), take time to “warm up”, lighting changes with age, fragile, strange looking, special versions needed to work with dimmer circuits.

Light Emitting Diodes (LED) bulbs use semiconductor technology to create light.  Because these are electronic components, they are much less fragile that incandescent or CFLs, but also currently more expensive to purchase.

  • Good – most efficient technology currently on the market, cool to the touch, good quality of light,  long lasting, robust.
  • Bad – expensive to initially purchase.  Special versions needed to work with dimmer circuits.

Who, Watt, Huh?

OK, but why can’t I just buy a “60 Watt” LED bulb.  Well, first let’s think about what a watt is – a unit of energy.  Specifying a light bulb’s output by the energy used is crazy.  It would be the equivalent if all gas powered cars more or less got the same MPG, (say 25MPG) as asking someone how far away a place was and instead of them answering “100 miles”, the actual distance, telling you “4 gallons”, the fuel consumed.  It works out the same, if all cars has the same fuel efficiency.  But along comes new technology such as hybrid cars that get 50 MPG.  When you ask someone how far the place is, it is still 100 miles away, but they have to answer “it is equivalent to 4 gallons in your gas powered car, but only 2 gallons in my car”.  Sheesh, just tell me it is 100 miles!

The unit of light output we care about is the lumen (equivalent to the mileage in the above analogy).  The precise definition of a lumen is actually quite complex, but for simplicity we can think of this as the “amount of light”put out by the light bulb, which is what we care about when we need to measure or compare brightness.  What makes CFL and LED bulbs much more cost efficient is that they have much better luminous efficiency (think MPG in the above analogy) compared to incandescent light bulbs, plus they last much, much longer.    A typical CFL will use about a quarter of the energy to produce the same amount of light as an incandescent bulb and a typical LED bulb will use more like 1/6th the energy of the same incandescent bulb.  In other words for the same amount of light, a 60W incandescent bulb bulb can be replaced by a 15W CFL or a 10W LED.  You should see the actual wattage on any light bulb package, but most new packages will more prominently list the lumens used and may have a “60W equivalent” or similar tag somewhere on the package.  You can imagine that if someone doesn’t understand this, they will think the 10W labeled LED bulb will be very dim compared to their 60W incandescent bulb. FYI, a 60W incandescent bulb puts out about 800 lumens and a 40W incandescent bulb around 420 lumens.  Good numbers to keep in your back pocket when you go shopping.

Wait, There’s More!

The power used (watts) and light output (lumens) are not the whole story.  For instance, aside from the physical characteristics of CFLs (e.g. their sometimes strange shape, and fragility), CFLs had other problems, some of which are noted above, in particular “quality of light”.

There are two things I’d like you to understand about “quality of light” – color temperature and CRI (Color Rendering Index).  First color temperature.  This is essentially how “white” the light is, something very important to me, since I am a photographer.  Our eyes tend to adjust such that we usually perceive the brightest thing we see as white.  But in reality the color of a “white” light bulb is very different from the “white light” outdoors.  If you look at an indoor light bulb while simultaneously gazing out a window, you will perceive the common incandescent light bulb as orange and the daylight as much bluer.  The actual color is measured in degrees Kelvin.  Higher numbers on this scale are “bluer”.  Perversely although their color temperature is higher, we describe them as “cooler” since they are more blue.  A typical tungsten light bulb will be about 2,700-3,000 degrees Kelvin.  Soft/warm CFLs are around 3,000, cool/daylight CFLs about 5,000 which is closer to the color of sunlight at noon (5,500), but not as high as an overcast sky (6,500).   LED light bulbs are offered in different colors – look for lower numbers (around 3,000) if you want something “warm”, i.e. closer in color to an old incandescent light bulb, or higher if you prefer closer to daylight.

But again, this isn’t the full story.  Turns out that different light bulb technologies don’t evenly reveal colors in objects.  You can have bulbs that have the same light output (lumens) and the same color temperature, yet the things lit by them will look different.  A good test of this is to get a paint palette or test pattern with all the colors and just look at it under the different lights.  Some of the colors will pop and others will seem very dull.

This is because although they may have a particular color temperature, the light bulbs may have a spike (or for that matter, a relative gap) in the color spectrum.  Fluorescent light bulbs are notorious for making things look greenish, which is particularly problematic for skin tones since it tends to make people look like ghouls.  The CRI (color rendering index) is a measure (out of 100) of how well a form of illumination can reveal different colors.  The standard incandescent light bulb has a CRI of 100 and so you can see all the colors of the palette.  CFLs vary widely here – a cheapo CFL can have a CRI of 50, but a high quality bulb can get as high as 89.  Typically I have only seen the CRI of a CFL listed on expensive bulbs, typically used for photographic applications.  Most LEDs are above 85 and thus their ability to render colors is much better than all but the best CFLs.  So even at the same level of light (lumen output), and same color temperature, the lighting from an LED will just look better than a CFL and should be virtually indistinguishable from that of the common old incandescent light bulb.

Over time, the difference is even more dramatic – CFLs get worse as they age.  While incandescent light bulbs might dim a little as they age, they will usually burn out first.  They also tend to get a little more orange as they age, but most people aren’t able to notice.  However CFLs may not only change noticeably in color, their CRI can drop too, i.e. as they age, things illuminated by them look even worse.

Economics

The typical incandescent bulb has a useable life of about 1,000 hours, versus about 10,000 hours for a CFL or 50,000 for an LED.  So you’d have to buy 50 incandescent bulbs (or 5 CFLs) for each LED. Right now a 60W incandescent bulb costs about $1 and a 60W LED replacement about $10, thus the purchase price is 10 times as expensive.  But, since it uses 1/6 the power to run, it is obviously much more efficient and less expensive in the long run, even if the up front cost is relatively high.  In fact, LEDs can be had for much less (about $5-6 at Costco, and even less at IKEA).  Depending on the cost of electricity from your utility (the more expensive your power, the more you’ll save), over the the life of an LED bulb, your actual cost (for the bulbs and all the electricity used) should be about 1/4 to 1/8 of that versus using incandescent bulbs.

Replacements for the standard 60W and 40W light bulbs will be the least expensive type of bulbs.  More specialized bulbs, such as spots, globes, etc. will cost more.  For instance, right now Costco sells a 2 pack of 65W spotlight (R30) replacements for $18.  See the next blog entry for more on decoding the light bulb alphabet soup.

My Two Cents

LEDs will continue to come down in price, but for now, my recommendation is that if you are not ready to take the plunge and replace all your old bulbs with LEDs,  pick a place in your house that you use a lot – the kitchen is probably the best option – and try replacing the main bulbs in that room with LEDs.  Also, if you have a room where you switch the lights on and off a lot, e.g. the bathroom, LEDs work much better than CFLs.  By the time the CFLs get fully warmed up, you may be ready to turn them off.

Some interesting factoids:

60W incandescent light bulbs are more efficient in the US versus Europe and other places that use 230V electricity. What?  Turns out at the 120 Volts used in North America,  our 60W light bulbs put out 850 lumens, vs. just 584 lumens in 130 Volt countries.  Or essentially our 40W light bulbs have about the same light output as a European 60W bulb!

Since I replaced almost all of the CFLs in my house with LEDs, I did a little testing to try to compare the brightness of some incandescent vs. CFL vs. LED bulbs.  I wouldn’t say these are “lab quality” results, but I did measure everything and I used a consistent testing methodology.  Interesting findings:

  • My new 400 Lumen IKEA bulbs were actually a bit brighter than the incandescent 40W bulbs they are supposed to replace.  The light output was actually as much as a new 100W replacement CFL bulb!
  • All of the CFLs I tested, (new and used) seem to put out less light than their incandescent or LED equivalents.  Most likely had I waited longer for them to get to “full temperature”, the light output would have improved a bit.
  • I had about a dozen CFLs of a particular type, all theoretically identical power and style, but of various ages. In testing them, I found their light output when measured the same way varied by as much as 8x!
  • I replaced these supposedly 65W replacement CFLs with 40W replacement LEDs and could see that the room appeared brighter.  By my testing, even the brightest of these CFLs was dimmer than the supposedly weaker LED, often by a considerable margin.

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