LED bulbs can bring heat

-September 27, 2016

I had a CFL fail the other day at our upstate house but when I went to the local hardware store to buy a replacement, there was nothing like it to be found. I did find a light emitting diode (LED) bulb though so I bought that and installed it with a plastic-shelled adapter having an on/off pull chain like this.

 


Sometime later, I got curious about how this new LED bulb was working out so I idly reached up to it and felt around. The spherical part of the envelope was just moderately warm to the touch but when I moved up the envelope toward the lamp's base, I started getting burned. High efficiency or not, this thing was running hot so I decided to do some testing.



 

Using a 100 watt incandescent bulb as a comparison tool, the end point temperatures were as shown above and the thermal rise properties of the two devices were the following.


 

These graphs were derived using the exponential curve fitting process described at "Fitting Exponential Equations to Data

The LED bulb is much heavier than the incandescent bulb. Its package cautions you to make sure that your bulb socket can support the heavier weight. Going along with that, we see a much longer thermal time constant for the LED bulb. It will take the LED bulb longer to reach final temperatures so if you do any checking up on this of your own, be patient about it.


It has crossed my mind that since the LED bulb has its higher temperature near the base (160°F) and since that base temperature is higher than the base temperature of the incandescent bulb (132°F), the plastic-shelled socket I used might not be a good choice for LED bulb service. Furthermore, although the LED bulb I examined has lower maximum temperatures than that 100 watt incandescent bulb, that 160°F temperature is high enough to do serious harm to unwary fingers!!


Some of the hype I've seen in advertisements for these things includes verbiage about good power efficiency which may lull one into a false sense of security about heating, but rest assured that if you get careless, an LED bulb can burn you.

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