Old eyes or bad bulbs? | Popular Woodworking Magazine
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I’m getting older, losing my near sight, and the world is growing dim. Sounds dire. And while it may be true, I think a big part of my problem is the light bulbs in my shop.  Unlike most of you, I have a photographic record of the lighting in my shop.  I recently compared photos I just took with photos I took several years ago.  There was a noticeable difference.  My shop is lit with long lasting compact fluorescent light bulbs.  These things may last a long time, but their performance degrades significantly over the course of a year or 2. You can see this by installing a new bulb next to an old one. Light bulbs have 3 characteristics we need to know about:

Color temperature, expressed in a temperature in degrees K , is the color of the light.  Generally, incandescent bulbs are yellower (we call them warmer).  Fluorescents are bluer (colder).  The color of the light isn’t a huge issue for us.  All you need to know is that if your shop is lit with fluorescent bulbs as mine is (and most shops are) colors may change when your work is moved to natural light or incandescent household lights.  I think the color temperature remains constant over the life of the bulb.

Color Rendering Index (CRI) is the percentage of the total light spectrum a bulb produces.  CF bulbs typically don’t produce as much of the spectrum as incandescents do.  This is what most of us don’t like about fluorescent light.  They reduce the color of everything they illuminate.

Lumens is the measure of how bright a light is.

Fluorescent bulbs significantly lose CRI and Lumens over time. Perhaps I shouldn’t wait until these things burn out before I replace them.  In my State, the big box home centers have collection points for used CF bulbs. If you’ve had CFL bulbs in your shop for a while, perhaps you should consider refreshing them.


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Showing 18 comments
  • John Verreault

    Excellent points Adam. My opthamologist says my vision hasn’t change yet, so I will follow your advice as my shop bulbs are getting into that age range and things do not look the same.



  • lawrence

    I know this is going to make some of you laugh, but I got a serious boost in my lighting when I cleaned off the outside of my bulbs and lights. The reduction in dust really showed.


  • 8iowa

    First of all I wish to tell you that I enjoyed our chat outside the classroom at the Last WIA. I’m looking forward to seeing you back in 2012.

    When I built my Upper Peninsula “Workshop in the Woods” I placed both incandescent and electronic ballast T-8 fixtures on the ceiling. This elevates the CRI in the shop, and frankly I feel that this is the most important index for woodworking shops, especially if colors of finishes are to be seen true.

    I also followed Henry Ford’s advice, “You can paint your shop any color as long as it’s white”. (At least I think he said something like this) Regardless, white walls and ceiling really help to reflect light and reduce shadows.


  • adrian

    Fluorescent lighting is complex, and the different products can vary in a variety of ways. Some fluorescent lights take a long time to reach full intensity after turn-on. Others don’t. It depends on the design.

    Regarding output, I’m not aware of a problem with the lumen outputs marked on CFL bulbs, though it doesn’t address dimming over time. But the so-called equivalencies are bunk. A standard single life 100W bulb generates 1700 lumens and yet you’ll see CFLs marked as “100 W equivalent” that only produce 1500 lumens, or less. If you compare lumen output directly and ignore any alleged wattage equivalency you should be able to get it right.

    Incandescent lights generate heat at 100% efficiency, if you measure efficiency by the conversion of electric energy to heat. This is a really bad way to use electricity, because that electricity was generated from some other energy source and then sent through lossy wires at probably something like 20% efficiency. A gas furnace can be 95% efficient. A heat pump is much more than 100% efficient (if you measure efficiency by the energy consumed divided by the energy added to the house). If you are in fact heating your house with resistive electric heat, like a giant light bulb, you should give some serious thought to switching.

    I have no connection to GE, but I’ve found their catalogs informative. Below are links to their compact fluorescent catalog and their linear fluorescent catalog:



    If you look at the lumen numbers, you’ll note that they give an “initial” lumen value and a “mean” lumen value. The “mean” value is labeled as the light output at 40% of bulb life. For a randomly chosen CFL I observed an initial lumens output of 1350 and a mean output of 1135. What does that mean? It means that when the bulb is 40% through it’s life it’s only producing 84% of the light it produced initially. And this will presumably decrease *roughly* the same amount again going down to the end of life, meaning something like 68% of full output at that point. This is quite a significant change, and one that could be troubling even to young eyes.

    If you take a look at a 4 ft long T8 bulb, the standard nominal 32 watt fluorescent you’ll notice that the lumen output only falls to 94% for the mean output. So there’s another reason beyond simple efficiency to really use the linear fluorescent fixtures if you can rather than using CFLs.

    I’m hoping for good, dimmable, LED lighting. But it doesn’t seem to be here yet. I’m curious, though, about color rendering. How can LEDs produce a good CRI without using the same phosphors as the fluorescent lamps? I thought that white LEDs worked essentially the same way, with a high frequency output being modified by phosphors. In fact, I heard that at least in some cases the LED might last 100,000 hours but the phosphor coating would only last 10,000 so the light wouldn’t maintain it’s color over time.

  • karincorbin

    At 60 years of age a person receives only 40 percent of the light inside the eye that they did at age 20.

    Add more lights to your workshop.

  • karincorbin

    At 60 years of age a person receives only 40 percent of the light inside the eye that they did at age 20.

    So year by year things will indeed be dimmer in your workshop even if you change the bulbs every couple of years.

    I am in love with the new fluorescent, electronic ballast 4 foot long tubes. I have changed my whole workshop out to 5000K fluorescent light bulbs and tubes.

  • Tony

    I’ve got old eyes too. I think they’re overly optimistic when they show lumens for the CFL’s. I’ve had better luck going up one when I replace an incandescent – I use a “75 watt equivalent” CFL to replace a 60 Watt incandescent.

  • Gary Roberts

    Shhhhhh It’s a secret! CFL’s have little itty bitty ballasts just like big ones do. Ballasts slowly fail over time and as they do, the lamp dims. Sometimes in cheapo bulbs the phosphor coating starts to fail too. Short term tests aside, it’s the long term results that matter. While short term high use testing is useful, it’s only when long term data is collected on the bulb, the bulb chemistry and the ballast that you know what is happening.

    It’s a downside to CFL bulbs that you can’t replace the ballast. I use them throughout the house and basement but I replace them every two years. For spot lighting I stick to old fashioned carbon arc bulbs. Just kidding. GE daylight.

  • joelm

    Get full spectrum florescents – changed my life. They do age but overall it’s a no brainer.

    I wrote a blog on it years ago.


  • jamrine

    Oh, and another thing to consider, dust on light bulbs is something not often considered, but there can be significant reductions in light output simply from bulbs getting dusty. This issue is magnified in something like a woodworking environment. Removing the bulbs and wiping them down from time to time is good for light quality and safety.

  • Mark Maleski

    C’mon, am I the only one using candles?


  • jamrine

    I work for a company that makes LED lighting devices, and we have done some extensive testing of different kinds of light bulbs using best practices of typical Energy Star and IES LM-79 testing for lamp durability. We ran bulbs at 3 hours on, 20 minutes off (90% on, 10% off) with a total of over 10,000 hours on time (this takes over a year), and tested the lights at intervals and recorded the luminous flux, color temperature, and CRI. I can confirm that color temperature does not change over time on the CFLs (or really any other lamp we tested). The 8000 hour CFLs we tested lasted for 9500 hours on average, but these were decent quality samples, and they were run in what is probably actually their ideal conditions (not turned off without ample warm-up time, kept at a 45 deg C ambient temperature, etc.).

    As far as CRI, the reason that fluorescent sources do not do well here is that there is a reliance on phosphors to shift the light into the visible spectrum and these are as discrete values, so instead of a nice smooth spectrum curve, you get spikes that attempt to approximate this curve.

    LEDs have the potential to approximate the full spectrum better than fluorescent sources, and as the efficiency (lumens per watt) and cost ($ per lumen) improve over the next 2-5 years, we will see a significant drop in the market for fluorescent sources, especially as rare earth materials become more scarce and expensive.

    I have some interesting public-domain charts I can supply if you are really interested, as the work we did was sponsored by the US Department of Energy.

  • Steve_OH

    I’m gradually switching over to LED lighting wherever I can. They’re expensive, but they last essentially forever. (My only LED lamp failure occurred when I made the mistake of using an LED lamp and a regular incandescent in the same fixture, and the LED device overheated.) The available CRIs aren’t great, but they’ve improved tremendously over the past few years.


  • SawdustWylie

    One more thing to consider – CFL’s seem to take a while to come up to full brightness. So if I switch on a task light for a quick task, it can take longer to come to brightness than the task. I finally went “overboard” and hung 20 of the four foot long dual-bulb fluorescent shop fixtures in my 750 sq. foot garage/shop. I put them on four different switches so I can turn on only what I need. The real solution was the bulbs – I put “Daylight” bulbs in, and with them all on, it really does look like natural daylight, great for finishing!

  • msiemsen

    My eyes are dim too. I wear bifocals as well. With the bifocals, I ordered mine to focus far away as with driving and from about 15 inches to the end of my hands where I typically work. They can also put the line of the bifocal where you want it. As far as I can tell most glasses are made for people working at a computer and not a workbench. As to lighting, I have always wondered why the incandescents get such a bad rap, they last a long time and give off good light. They are supposed to be inefficient giving off way more heat than light.I heat my home most of the year and during the hot season the days are much longer and I don’t use lights, so I figure for me incandescents are almost 100 percent efficient. The CFLs work OK but I have yet to have one last 1/2 as long as they claim they do. I have 4 foot fluorescent lamps in the shop and they require replacing as well.
    Happy Holidays!


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