Most of us learned to select our lighting by choosing an incandescent light bulb that we considered “bright enough.” That brightness is roughly indicated by wattage (W)—a measurement of how much energy the bulb uses. Comparing wattage has been a pretty good way to choose a good incandescent light bulb for the desired illumination level (usually a 40W, 60W, or 75W bulb).

However, new developments in lighting products give us many more choices than we had ten years ago—and knowing how much energy a bulb uses doesn’t tell you much about the appearance of the light it casts. Fortunately, more precise information is available on Lighting Facts labels, found on all new lighting products.

Here are some terms to look for:

  • Lumens (Lm): light output. High-efficiency bulbs supply more lumens per watt than lower efficiency bulbs. In other words, they use less energy, so you get more light for less money.
  • Color Temperature: the hue of seemingly “white” light, ranging from “cool” (bluish) to “warm” (reddish), expressed in degrees Kelvin (K).  In general, cooler light is best for visual tasks, while warmer light enhances flesh tones. For most uses, you’ll probably want a color temperature of 2700K to 3000K.
  • Color Rendering Index (CRI), also referred to as ”color accuracy”): a measure of how faithfully a given light source reproduces particular colors in relation to an ideal or natural light source. As a reference point, sunlight and incandescent light bulbs have a CRI of 100. When buying compact fluorescent lights (CFLs) or light-emitting diodes (LEDs), look for a CRI of 80 or more to get good color rendition. With a CRI below 80, some colors may shift in tone or lose saturation.

You may also come across the term foot-candle. While “lumens” describes the output of a light source, “foot-candle” refers to the intensity of light falling on a given surface.

Also consider the way the bulb and fixture distribute light and where the unit is placed in the room. Overhead fixtures and bulbs that cast light in all directions are commonly used for ambient light. Cove lighting is a type of indirect lighting that involves incandescent or fluorescent lights concealed in a reflecting trough near the ceiling; the light is usually reflected off the ceiling or wall. Directional lighting is designed to cast a narrow beam; it’s good for task and accent lighting. Using the right fixture for the job puts those lumens where you need them.

How Many Lumens Do You Need?

The answer depends on the size of the room and the color of your decor. Here are some rules of thumb (Lm/sf = lumens per square foot):

  • Dining : 5–20 Lm/sf
  • Living : 5–20 Lm/sf
  • Kitchen: 5–50 Lm/sf
  • Bathroom: 5–50 Lm/sf
  • Office: 10–50 Lm/sf
  • Outdoor : 0.3–1.5 Lm/sf

Apply the lower end of the range for ambient lighting and the higher end for task and accent lighting. Older occupants generally require more light—as much as 100 Lm/sf for sewing or studying.

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