Specific Lighting Semantics

Shoppers should familiarize themselves with the correct terminology when they’re looking for lighting. “Lightbulbs” are “lamps”—mechanisms that consume energy and deliver light. Lamps are typically a part of another device, which controls the way the light is distributed into the space. This device is called a “light fixture” or “luminaire.” The term “light source” may refer to either a lamp or a light fixture. 

There are several other terms to become familiar with when evaluating and comparing lamps and light fixtures. Many reputable manufacturers publish data in product specification sheets (usually available online). Sometimes, this information can be found on the product packaging. Look for the following specifics:

Watts: A measurement of the amount of power a light source consumes.

Lumens: A measurement of the amount of light a light source produces.

Efficacy: A measurement of lumens produced per watt consumed (LPW). For example, if you have a 100 W lamp that produces 1,800 lumens, divide the lumens by the watts and you will get the measured “efficacy”—18 LPW. 

Correlated Color Temperature (“CCT”; measured in degrees Kelvin): A measurement of the “warmth” of a light source. For example, the yellow warmth of a candle measures 1,500 Kelvin. A standard household incandescent A-lamp measures about 2,700 K. Halogen sources measure approximately 3,000 K, while fluorescent sources can range between 2,700 K and 5,000 K. White LED sources have an even greater range, spanning 2,700 K to 8,000 K. For a comparison, noon sunlight measures 5,500 K. North light (under a blue sky) measures 8,000 K. The bulb’s Kelvin rating, however, does not tell you anything about how accurately the light source renders colors in the environment (see CRI, below). 

Color Rendering Index (“CRI”): A measurement of how well a light source renders colors in the environment. CRI is not a perfect measuring system, but in general, the higher the number, the better the color rendition. Select lamps with a CRI between 80 and 100 to make people and things look their best. Note that incandescent and halogen sources are always rated at 100, even though incandescent sources are deficient in the blue end of the spectrum. 

Beam Spread: If the light source you are considering is a “point source” (meaning the light is directed primarily in one direction) like an outdoor floodlight (PAR lamp) or an MR16 halogen lamp, then you want to carefully select the appropriate beam spread for your application. Typically, you will find the following options: spot—10°; narrow flood—25°; flood—40°; and wide flood—60°. This means the primary intensity of the beam will fall within this conical field of measurement. 

Lamp Life: A measurement of how long the lamp will operate in hours before it either extinguishes, shifts to an undesirable color, or produces less than 70% of its rated lumen output. 

Dimming: It’s important to consider whether a light source is dimmable and if there are added costs to dim the product. Also consider that some LED and CF sources have limited dimming ranges and do not shift to a warm tone when dimmed. 

—Julia Rezek