How to Select a Light Bulb
Purchasing a light bulb ought to be easy, but with the introduction of new lighting technologies, more options are available. Following are three questions to ask:
- 1. What category style of lamp is appropriate (decorative, general use, etc...)?
- 2. How much light (brightness) is needed?
- 3. Select your preference for other features (color temperature, color rendering, Internet-connected, etc..).
Light Bulb Categories, Styles, and Bases
The shape of light bulbs (also known as "lamps") fall into a handful of broad categories, each of which has a letter value. Common light bulbs (also known as omnidirectional) are in the "A" category. Following each of these letters is a numeric value, representing the width of the light bulb in eighths of an inch. An A19, therefore, is a general use light bulb that is 19 eighths of an inch wide. The higher the numeric value, the larger the diameter of the light bulb.
- A Lamps: (arbitrary/standard, projecting light in all directions)
- ST Lamps (spherical tubular, which is a vintage style) Decorative
- B Lamps: (conical shape with blunt tip)
- BA Lamps: (conical shape with bent tip)
- F Lamps: (conical shape with flame pattern in the glass) Globes
- G Lamps: (globes) Reflectors
- BR Lamps: (bulbous reflector, delivering a soft, diffused light)
- MR Lamps: (multi-faceted reflector, very compact, often used in track lights)
- PAR Lamps: (parabolic aluminized reflector, delivering an intense light, often used outdoors) Linear
- T Lamps: (tubular lamps)
The base of most lamps offered are E26 medium base lamps. If a lamp base has a different style it would be noted through the abbreviations below, which reflect some of the most common base styles:
- E26: (Medium (or Standard), the most common socket type for standard light bulbs)
- E12: (Candelabra, a small socket used in decorative fixtures and chandeliers)
- GU10: (a base with 2 tabs 10mm apart, locked into place with a twist.)
- GU24: (a base with 2 tabs 24mm apart, locked into place with a twist.)
- GU5.3: (a base with 2 pins 5.3mm apart, pressed into place)
- Medium Bi-Pin: (a base often used in commercial fixtures with linear lamps)
Lumens is a measure of light output. The higher the lumens value, the brighter the light. In 2007 the Energy Independence and Security Act (EISA) included provisions to improve the efficiency of general service light bulbs by at least 25%. Pre-EISA a 1,600 lumen general use incandescent lamp would typically consume 100 watts of electricity, but post-EISA a general use lamp could consume no more of 72 watts of electricity. Following are common lumen ranges, and typical equivalencies. The pre/post EISA references pertain to incandescent lamps.
- 1 lumen: (candle)
- 150-250 lumens: (25w incandescent, 5w CFL, 3w LED)
- 251-450 lumens: (40w pre-EISA, 29w post-EISA, 9w CFL, 4w LED)
- 451-800 lumens: (60w pre-EISA, 43w post-EISA, 15w CFL, 9w LED)
- 801-1,100 lumens: (75w pre-EISA, 53w post-EISA, 20w CFL, 13w LED)
- 1,101-1,600 lumens: (100w pre-EISA, 72w post-EISA, 23w CFL, 18w LED)
- 1,601-2,000 lumens: (125w incandescent, 30w CFL, 20w LED)
- 2,001-2,600 lumens: (150w incandescent, 42w CFL, 30w LED)
The correlated color temperature (CCT) is the color of a lamp, measured in degrees Kelvin. The lower the value the "warmer" (more orange/red) the color of the light, with higher values being "cooler" (more white/blue). Most of the lamps offered have a color temperature of 2,700 degree Kelvin (soft white). If a lamp has a different color temperature, it will be noted. The following reflects the categories and terminology recommended by the United States Environmental Protection Agency's ENERGY STAR program.
- 2,200 K: Amber White
- 2,500 K: Sunrise/Sunset White (color of sunrise/sunset)
- 2,700 K: Soft White (color of typical incandescent light)
- 3,000 K: Warm White (color of typical halogen light)
- 3,500 K: Neutral White (color of morning/evening sunlight)
- 4,000 K: Cool White (color of moonlight)
- 4,100 K: Cool White
- 5,000 K: Daylight
- 5,500 K: Daylight (color of midday sun)
- 6,500 K: Daylight (color of a cloudy sky)
Some new lamps coming into the market are able to deliver a range of color temperatures (and colors). "Color tunable" lamps allow the user to change the color appearance of the lamp. "Color shifting dimmable" lamps automatically lower the color temperature as the lamp is dimmed. "White-tunable" lamps allow the user to change the color temperature of the lamp along the correlated color temperature range. With "full color tunable" lamps the color of the lamp can be changed from white to other colors (red, green, blue, etc..).
The color rendering index (CRI) uses a scale of 0 to 100 to reflect how accurate the colors of object illuminated by a light appear. The higher the CRI value, the more vibrant (less washed out) an object's colors will be. Most lamps offered have a CRI of 80-84 (good). If the CRI is outside of this range it will be noted.
- CRI <80: Poor (acceptable for outdoor use)
- CRI 80-84: Good (acceptable for most indoor applications)
- CRI 85-90: Very Good (acceptable for most indoor applications)
- CRI 91-100: Excellent (retail store and museum-quality)
Following is a comparison of various light technologies.
- Incandescent Light Bulb Typical Life: 1,000 hours
- Compact Fluorescent Light Bulb Typical Life: 10,000 hours
- LED A Lamp Typical Life: 15,000-25,000 hours
- LED Decorative Lamp Typical Life: 15,000-25,000 hours
- LED Directional Lamp Typical Life: 25,000 hours
To determine the expected life of a product, use the formula below:
- Lifetime (years) = ([rated product life]/([typical use hours per day]*365))
The wattage reflects the amount of electricity consumed. A kilowatt hour (kWh) is the unit of measure that electric rates are based on, which is the same as using 1 watt of electricity for 1,000 hours, 10 watts for 100 hours, or 100 watts for 10 hours. To determine your annual savings...
- Step 1: Calculate the kilowatt hour consumption of the light bulb being removed:
((([watts]*[average hours of use per day])*365)/1,000)
- Step 2: Calculate the kilowatt hour consumption of the light bulb being installed:
((([watts]*[average hours of use per day])*365)/1,000)
- Step 3: Subtract the Step 2 result from the Step 1 result to determine the kWh savings
- Step 4: Multiple the difference by your local electric rate to determine the economic savings ($0.10 was the U.S. average across all customer types in 2015).
And, to determine the dollar savings over the expected life of the product, multiply the result from Step 4 by the expected product lifetime determined in the previous section.
- (43 watts x 2 hours) x 365)/1000 = 31.39 kWh used annually
- (9 watts x 2 hours) x 365)/1000 = 6.57 kWh used annually
- 31.39 kWh - 6.57 kWh = 24.81 kWh saved annually
- 24.81 kWh x $0.10 = $2.48 saved annually
EXAMPLE: The calculation associated with removing a 43 watt incandescent light bulb that is used 2 hours a day and replacing it wth a 9 watt LED rated to last 25,000 hours would be....
A 25,000 hour lamp used 2 hours per day will last 34.2 years ((25,000 hours / 2 hours) / 365), so the product lifetime savings associated with installing a 9 watt LED would be $84.82 ($2.48 x 34.2 years), assuming no change in the electric rate.