LEDing it hang out: The downside of higher efficiency

-January 20, 2014

It's not news that the venerable incandescent light bulb, which has served us so well for over 100 years, is on its way out. Through a combination of legislative mandates, local building-code imperatives, and operating-cost pressure, there's been a sequence of phase-outs, starting with 100W bulbs and working down to 75W, 60W and so on. (Strictly speaking, these rules don't exclude incandescent bulbs, they just require that bulbs achieve certain efficiency levels which incandescents can't meet; if you could come up with a sufficiently efficient incandescent bulb, you'd make a fortune!)

This isn't the place to argue the technical virtues and vices of LEDs and CFLs as replacements, or the broader economic and environmental effects; those are discussions for another time and place. But as the switchover proceeds, it's interesting to review how the 90% inefficiency of the incandescent bulb - and the resultant heat it gives off - was actually used to advantage in many applications. There have been many reports, such as a recent one from Canada (see "Incandescent bulb ban leaves bird care centre with dim hope"), where the basic 100W bulb was used as a heating element that was cheap, easy to obtain, and easy to replace when it burned out (as most heating elements do).

Even better, as a resistive load, the incandescent bulb is easy to control and regulate. No matter that it has a highly nonlinear input/output transfer function - as long as you have a closed loop with a temperature sensor in the system, you had the makings of a pretty decent controllable heater.

The law of unintended consequences (one of my favorite "laws") even extends to low-cost, mass-market items such as the Hasbro Easy-Bake toy oven, which the company has been making for decades with minimal few changes. Key to the design was the use of a standard bulb as the heating element; again, it was cheap, easy to source, easy to replace. However, the oven had to be completely redesigned with a custom heating element in place of the bulb (see "Easy-Bake loses its bulb, gets a makeover"). While in the broader scheme of things, this is just a toy and re-designing it is not a major disruption, I'm sure there are many applications where such a redesign or retrofit is a far bigger deal.

Reality is that there are many times where the downside of a product or technology has been flipped around and used to advantage. One of the many lessons I took away many years ago from the excellent 1978 TV series Connections by James Burke is that in most cases, progress comes when an application adapts advances or developments from other, unrelated areas - even the ones with shortcomings. (If you haven't seen this series, I urge you get to get it as a DVD, or look for the YouTube segments; it's well-done, educational, and also thought-provoking.)

To those who welcome the loss of the incandescent bulb and its severe inefficiency, I wonder: what else is being lost with it, via attributes and roles that you don't recognize? Have you ever been involved in a design where you took advantage of what everyone else saw as a weakness of a component or approach, and actually used it to your advantage?

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