Hidden costs of Light bulbs

Posted on Feb 15, 2009 by Paul White

If you read a previous post I wrote, you know I was figuring out the benefits of changing out all the light bulbs in my house to the newer compact flourescents.  The amount of energy you save by changing out a single light bulb is amazing. 

As I was switching out the old bulbs, I noticed how they were still hot to the touch after being off for several minutes.  The housings around the bulbs were also quite hot.  I know that standard light bulbs make alot of heat, but I had no idea how inefficient they were until I did a little research.

Its said that a standard incandescent bulb only converts 2% of its energy into light.  The other 98% goes into heat.  So essentially every 60 watt light bulb in your house is a 58 watt heater.  This means that your AC has to work over time to keep up with the heat each of these bulbs generates. 

I decided to work the math and figure out how bad it really is.
In our simulation we will figure out the numbers for a 60 watt light bulb running for an hour
Assuming a 98% conversion of the energy into heat we get
58 watts = 198 BTU/ hr

Cooling and Heating efficiency is measured in SEER.  In my house we have a 10 SEER central AC unit.  This means that our Air Conditioner makes 10 BTUs/ WattHour.
198 BTU / 10 BTU = 19.8 WattHour concsumed by AC.
This math doesn't make sense.  as I would assume that a 58 watt heat source would need at least 58 watts of cooling.  Non the less it proves that the cost of a standard 60 watt light bulb is much higher than originally thought.

Other good articles:

1. Light Efficiency, Heat, and WattageTo a home-owner, the "standard" is the Edison filament light bulb. It uses a lot of its watts input producing heat output. To get the same amount of lumens
2. Incandescent light bulb - Wikipedia, the free encyclopediaSome applications of the incandescent bulb make use of the heat

   .....

   An incandescent lamp which gives 93% or less of its initial light output at 75% of its
3. About Compact Fluorescent light bulbsRemember a CFL puts out 4 times the light per watt over regular incandescent light bulb. Plus will also reduce heat output. For example the fixture says MAX
4. Watts, heat and Light: Measuring the Heat Output of Different LampsAccording to the Wikipedia online encyclopaedia, a 100 watt bulb is 2.1% efficient. In other words, it produces about 2 watts of light and 98 watts of heat.
5. LED light bulbs (NOT)Not all bright LED light bulbs are able to replace current bulbs. Other: Heat output, heat sinking - built-in or specially made, wattage, brightness,
6. Lightbulb TechnologyNov 22, 2006 25 Watt Compact Flourescent "Transformed" light bulb technology. Light Output. Energy use. Heat output (inefficiency)
7. The Great Internet Light Bulb Book, Part IIn a 120 volt, 100 watt "standard" bulb with a rated light output of 1750 lumens, The reason is that a fill gas conducts heat away from the filament.
8. Light Bulb & Lamp Science Fair Projects & ExperimentsCompare the efficiency of different types of light bulbs (incandescent, halogen, fluorescent) by testing the light intensity and heat output of the bulb.
9. COMPARISON OF LIGHT AND HEAT OUTPUTS BETWEEN TWO DIFFERENT BRANDS (They would really put out the same light and heat as clear bulbs of the same wattage but the frosting affects the output). DISPLAY This display is set up

Discussion

name
Email	Needed to confirm comment, but not made public.
Website

	Email me when someone comments on this blog

When you Post your Comment, you'll be sent a confirmation link. Once you click this link your thoughts will be made public.. Posts that are considered spam will be deleted, Please keep your thoughts and links relavent to this Article