The Energy Audit-Light Bulbs

The first commercially available incandescent light bulb was a product of Thomas Edison and has been available since the late 1800’s.  They remained, for the most part, unchanged for the first 100 years.

A glass enclosure filled with an inert gas and a wire filament inside that glows when electricity is applied. They are simple, cheap, and INEFFICIENT.  Approximately 5% of the electricity used by an incandescent bulb is used to create light, the remaining 95% is heat produced by the resistance of the electricity in the wire filament.

Incandescent bulbs are scheduled to be phased out in 2020 in the United States.  The state of California, as of 1/1/2018, will no longer allow incandescent bulbs manufactured after that date to be sold in the state.  The old light bulbs I grew up with have changed.  The compact florescent bulb, that curly piece of glass which was toted as more energy efficient and longer lasting than it’s predecessor started a much needed change in light bulb efficiency.  The last few years the light emitting diode bulb has become king.  These bulbs are much different than the old incandescent.  They have much different light outputs, colors and electrical consumption.  A new lesson must be learned.  Let’s start with a few definitions.

  • LED bulb-light emitting diode light bulb. The light emitting diode is a semiconductor that creates light. The LED bulb became commercially available in 2008.
  • CFL bulb-compact florescent lamp. A process where excited mercury electrons radiate ultraviolet light, which is converted to visible light when striking the coating of the florescent lamp.  First available in the early 1980’s, CFL bulbs were the first energy efficient replacement for incandescent bulbs. Because of the mercury content, recycling is recommended when disposing of a CFL light bulb.
  • Watt-a unit of power, used to describe the rate of energy transfer.  Basically, a watt is how much energy a device uses and the unit in which you are billed for this energy.  1000 watts is equal to 1 kilowatt hour (kWh), which currently costs around $.12 in my area.
  • Lumen-the visible light output of a source, in this case, a light bulb.
  • Kelvin-in the case of lighting, Kelvin is the color rendition the bulb produces, or its color temperature.  2000-3000 Kelvin is a warm color, 3000-4500 Kelvin is a cooler color, and 4500-6000 Kelvin is daylight.

Most of us who remember lighting before the LED and CFL bulbs associate light output by watts.  Those of us who grew up using the old light bulb know how much light a 100-watt incandescent bulb produces.  An equivalent LED or CFL bulb create almost an equal amount of light but use much less power.  Let’s compare a 100-watt incandescent bulb, a CFL bulb and a LED bulb.  A 100-watt incandescent bulb produces around 1600 lumens.  A compact florescent bulb that produces an equal amount of light will consume about 23 watts and a light emitting diode bulb, around 15 watts.  I’ve compared the energy consumption of each of the bulbs assuming a three hour per day run time over a one-year period.  Cost of electricity is $.12 per kWh.

First the incandescent bulb, 100 watts of power used will cost $8.64 per year, the CFL bulb uses 23 watts and costs $1.99 per year.  Lastly, the LED bulb uses 15 watts of power and costs $1.30 per year.

Another advantage of CFL’s and LED bulbs is their life span.  An incandescent bulb is expected to last around 1,200 hours, the CFL should last 10,000 hours (most don’t last nearly as long as rated), and LED around 25,000 hours. I’ve heard a lot of complaints about CFL bulbs over the years.  Longevity and full light warm up time are common complaints.  I’ve even heard of a CFL starting on fire.  Because of these concerns, along with the small amount of mercury in CFL bulbs, and the reduced cost of LED bulbs, my recommendation over the past couple years has been to make the switch to LED’s.

The lumens, or light created by the bulb and the wattage, or power consumption of the bulb are related.  The higher the wattage, the more lumens.  This is true of all light bulbs.  Using an LED bulb as an example, a 9 watt bulb will produce 800 lumens.  About the equivalent of a 60 watt incandescent bulb.  A 15 watt LED bulb produces 1600 lumens, the equivalent of a 100 watt incandescent.

We’ve discussed the lumen rating of a bulb, how about Kelvin, or the color of the bulb.  2000-3000 Kelvin is a soft white bulb producing colors that are orange to yellow white.  This color of bulb work best for most locations around the home.  3100 to 4500 Kelvin is considered cool white, more of a neutral white and is often used for task lighting.  4600 to 6000 Kelvin is daylight or a bluer white and is mostly used outdoors or as task lighting.  5780 Kelvin is considered the color of the sun or true daylight.

Almost every style bulb, choices in lumens, and Kelvin color rendition is available in an LED bulb.  My recommendation for replacing a questionable bulb is bring the old bulb to the store.  Be sure to note if the bulb is on a dimmer switch.  Some LED bulbs are not dimmable.

A question I often get is should I go out and replace all my bulbs with LED’s? Probably not.  Even with the reduced cost of the bulb, replacing every bulb in a home would be a sizeable investment.  Start with the most used bulbs in the home.  Reading lamps, kitchen and dining room fixtures, and bathroom lighting are good places to start.

Recessed lighting bulbs are also good candidates for replacement.  An incandescent bulb in a recessed can fixture creates a lot of heat.  Many of these recessed fixtures are installed in attic spaces, and the heat from the bulb can act like a chimney, drafting air from the conditioned space into the attic.  Replacing a hot incandescent with the cooler operating temperature of an LED bulb can reduce, though not eliminate, this condition.

Outdoor lighting could also be replaced.  Many outdoor lights have high wattage bulbs that may be on from dusk to dawn or motion activated.  Be aware, some outdoor lighting, such as high-pressure sodium and metal halide fixtures, do not have an LED bulb replacement and the entire fixture might need to be exchanged.

That’s the basics of light bulbs. Questions or concerns? Post them in the comments section of the Northern Built blog.

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