Save Energy — Lighting

Since Edison’s design of a practical light source, lighting as grown to be a vital part of our home. Lighting allows you to function in your home at night as well as provide security. Because of this the light bulb had become an overlooked household item. But because of its energy use and new types of light bulbs, lighting has been a focus area for saving energy.

Your Home Energy Living Plan

  • Turn off lights when not in use.
  • Clean dust off of bulbs.
  • Use task lighting when reading.
  • Use lowest wattage possible for function.
  • Convert to Compact Fluorescent Lighting (CFL).
Impact of Your Energy Saving Actions

10% of the average US home’s annual utility bill goes to lighting. If you find lights that are on for long periods of time, your percentage can be higher. Simply minimizing the use of lights can have an impact. If you replace bulbs with CFL type bulbs, then the contribution of lighting to your bill can be sharply reduced.

How Energy is Lost

To generate light, energy is needed. That energy comes from electricity. Light bulbs produce light and also produce heat. Some light bulbs like incandescent only convert 10% of the energy to visible light. With bulbs costing about 25 cents most people were not concerned about the low efficiencies. Also just a few years ago other options were too expensive.

Characteristics of Lighting

The traditional incandescent light bulb uses a tungsten element (filament) heated by electrical resistance. This element heats to about 2000 to 3300 degrees Kelvin. This high temperature radiates energy but only about 10% is in the visible range of wavelengths. The rest is heat radiation. Each time you turn on the light, its filament goes from room temperature to the high temperature in a very short amount of time. This rapid increase in temperature causes the filament to stretch and bend slightly. This makes it brittle and will eventually break. That is why a bulb usually burns out when you turn it on. If the bulb was left on, then it would last for a very long time. An incandescent light bulb at a fire station in Livermore, California has been on continuously for over 100 years.

Some people have suggested it is more cost effective to leave the light on. However, the energy costs for leaving on the light is greater than turning the light off and replacing it when it burns out.

The amount of visible light emitted by a light bulb is measured in lumens. A 100 watt incandescent light bulb emits about 1700 lumens. Since it is the purpose of the light bulb to produce visible light (lumens), they can be rated by the lumens they produce divided by their wattage. This is called efficacy. A 100 watt bulb has an efficacy of 17.0 (this is not a percent, it is lumens per watt). The higher the efficacy, the better. A 60 watt incandescent bulb has an efficacy of 14.5.

As other light source are examined the lumen output and efficacy are important. Another type of light is the fluorescent light bulb. A tube containing mercury in argon or neon gas is turned in a plasma when exposed to electric current. The plasma emits ultra-violet light which illuminates a phosphorous coating on the inside of the tube wall. The phosphor fluoresces emitting light in the visible range. As current flows through the bulb, its electrical resistance decreases. This allows more current which in turn lowers the resistance. Without any other device the bulb would quickly burnout. A device called a ballast is needed to regulate the current. Fluorescent bulbs with an electronic ballast can have efficacies around 60. This is 3-1/2 times better than a 100 watt incandescent bulb.

Fluorescent lighting has been around since the late 1930s and has been mostly used in commercial and industrial buildings. They were not popular for residential use because of their size, style, and problems with humming and flickering. Technology has come to the rescue with the development of the compact fluorescent bulb (CFB or CFL). Being the same size as typical incandescent bulbs, makes replacing easy. The ballast is electronic so it is small and eliminates hum and flicker. These bulbs have become inexpensive and compete well on price alone when considering life of the bulb.

Incandescent bulb are rated for 900 to 1000 hours of operation, while the CFL is rated between 10,000 to 15,000 hours of operation. Compact fluorescent bulbs will last about 8 to 10 time longer than incandescent (rated life of the bulbs can vary). With CFL prices around 2 to 3 dollars (shop around for best price). Just based on cost over time alone, CFL can be more cost effective.

Manufacturers are attempting to combine LED lights for residential use. Light Emitting Diodes (LED) can have efficacies in the 90s. However, LED bulbs have low lumen output; usually less than 100. Cost can increase extremely with higher lumen outputs. While LEDs use less energy than CFLs, their high cost make them a future advance.

Energy Solutions Explained

There has been much media coverage of higher efficiency lighting options. However, the best way to save energy is to turn off the light.

Dust can accumulate on the bulb. This reduces the light output of the bulb. When it burns out you may have the tendency to buy a larger wattage bulb because you think the old bulb was too dim. Dirt also insulates the bulb. It will burn hotter and not last as long.

Overhead lights can have 3 or 4 sockets rated for 60 watts each. This is a total of 180 or 240 watts. One light fixture near the place you use the light would only be 60 watts. Even a 100 watt light bulb uses less energy.

Using 40 watt bulbs instead of 60 watt will save energy; if you can accept the lower light level. However, a 100 watt light bulb is more efficient than a 40 or 60 watt bulb. Use a larger wattage bulb instead of several smaller bulbs.

At current prices, CFL can be more economical than incandescent bulbs based only on cost over time. In this case all energy savings are true savings. The higher cost of CFL is offset by the cost of replacing the incandescent bulb. Therefore none of the energy savings goes to compensating for initial cost.

Speak Your Mind