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An Illinois River Almanac

Jason Haupt's Energy and Environment Blog

Let there be Light

Posted by Jason Haupt - Energy

I love the fall. Football has started, the weather is cooling off, the leaves are beginning to turn, and the days are getting shorter. With the days getting shorter, that means we are going to be using the lights in our homes more often. If you have been to the store and looked at light bulbs lately, you will know that there seems to be an endless choice of light bulbs from which to choose. So what should you choose and how do you know what bulb will give the right amount of light most efficiently?

There are several aspects of lighting that should be understood when you are selecting the lighting for your home.

First let's talk about efficiency. When you first look at a light bulb, it has a WATT rating. This is a measure of the amount of energy it requires to provide light. The lower the number is the more efficient the light bulb.

Now let's talk about the quality of the light. There are a number of factors that contribute to the quality of the light. First there is the color temperature of the light. This has nothing to do with the amount of heat that a bulb puts off, but it refers to the color of the light. Yellow and red colors are warm and blue and green colors are cool. Light color is measured in Kelvins (K) and the higher the temperature the cooler the color. When selecting the bulb, keep in mind that warmer colors are preferred for living spaces. Second there is color rendition. This is a measure of a light source's ability to render color the same way that sunlight does. This is measured on a scale of 1 to 100 with 100 being the highest. Anything above 80 is considered acceptable for indoor lighting applications.

The final thing that needs to be considered is quantity of light that is being produced. Each light bulb will produce a certain amount of light. This is measured in a couple of ways. The Lumen is a measure of light emitted by a lamp. A Footcandle is a measurement of intensity of illumination. A Footcandle is the illumination produced by one Lumen distributed over a 1 square-foot area. For most home uses 30 to 50 Footcandles is sufficient.

With this knowledge in hand, let's talk about the types of bulbs available. There are three major types of light bulbs available. The Incandescent is most common, but the least efficient.Three types of Incandescent bulbs are available in stores: the Standard "A" bulb, the Energy Saving Incandescent, and Reflector. Of these three types, the most efficient is the Energy Saving Incandescent bulb. Fluorescent bulbs are also very common and come in three varieties: the Straight Tube, Compact Florescent (CFL) and the Circline. The final type is the Light-Emitting Diodes (LED). Two varieties can be found: Cool and Warm White LEDs. Below is a chart from that shows the different type of bulbs and the characteristics of the bulbs.

The Department of Energy has these recommendations for new homes:

Energy-efficient lighting design principles include the following:

  • More light is not necessarily better: light quality is as important as quantity
  • Match the amount and quality of light to the performed function
  • Install task lights where needed and reduce ambient light elsewhere
  • Use energy-efficient lighting components, controls, and systems
  • Maximize the use of daylighting.

Here are some basic methods for achieving energy-efficient indoor lighting:

  • Install fluorescent or LED light fixtures for all ceiling- and wall-mounted fixtures that will be on for more than two hours each day, such as kitchen and living room, bathroom, hallway, and other higher-demand locations.
  • Consider installing fluorescent or LED fixtures, rather than using fluorescent or LED replacement lamps in incandescent fixtures.
  • Use CFLs or LEDs in portable lighting fixtures that are operated for more than two hours a day.
  • Use ENERGY STAR® labeled lighting fixtures.
  • Use occupancy sensors for automatically turning on and off your lights as needed.
  • Consider light wall colors to minimize the need for artificial lighting.
  • If you are using recessed lights in a ceiling with an unconditioned space above it, use only Underwriters Laboratory (UL) approved fixtures that are airtight, are IC (insulation contact) rated, and meet ASTM E283 requirements.

For more information please visit:

Lighting Comparison Chart

Lighting Type



Color Rendition Index

Color Temperature



Standard "A" bulb



98–100 (excellent)

2700–2800 (warm)


Energy-Saving Incandescent (or Halogen)



98–100 (excellent)

2900–3200 (warm to neutral)





98–100 (excellent)

2800 (warm)



Straight tube



50–90 (fair to good)

2700–6500 (warm to cold)


Compact fluorescent lamp (CFL)



65–88 (good)

2700–6500 (warm to cold)






Light-Emitting Diodes

Cool White LEDs



70–90 (fair to good)

5000 (cold)


Warm White LEDs



70–90 (fair to good)

3300 (neutral)


Chart taken from:

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