Lighting Basics for Your Basic Bulb Purchase
As energy efficient lighting evolves so does the confusion about what you are buying. How does at 75W incandescent bulb compare to a CFL or LED bulb? For years the most I had to rely on was the wattage comparison on the packaging, but there's more to the comparison than that. And sometimes there's not even that information to rely on.
How is a hotel expected to tend to a quality guest experience and energy conservation if manufacturers provide inadequate information for good decisions? Buying energy efficient light bulbs isn't as easy as it should be. How do you compare an incandescent light bulb to a CFL to an LED? What do the different terms mean?
What else do you need to pay attention to other than the obvious energy savings, as illustrated by the wattage? What does it take to have a pleasing light for good guest experience? Color temperature (spectrum of light), CRI (color rendering index), and lumens.
Color temperature is a quantitative measure. Simply put it refers to "soft white", "cool", and "daylight" like terms. Color temperature is generally represented in Kelvin (refers to absolute temperature; 0 degrees Kelvin refers to the point at which no heat energy remains in a substance, and 273.15 degrees Kelvin equals 0 degrees Celsius), but mired (1 million divided by the color temperature in Kelvin) is also used at times.
|warm/soft white||<= 3200K||daily living; bedroom, rec room, living room, family room|
|cool/bright white||3200-4000K||work; garage, hobby room, kitchen, bathroom|
|daylight||>=4000K||detail; reading or where you want accurate color rendition|
The activity you expect in a given room helps guide you as to the color temperature you select. Some decorators may also determine the color temperature impacts their design so try to persuade you about the bulb you select.
Color Rendering Index
CRI is a quantitative, not subjective, measure of the ability of a light source to reproduce the color of various objects faithfully in natural light. CRI refers to the spectrum of light, or it's a measure of the full range of colors visible to the human eye; temperature impacts CRI so must be considered if accuracy is important to your bulb decision.
The CRI of incandescent and LED bulbs are pretty close, while CFLs are missing a bit in the blues. You want your CFL to have a value as close to 100, over 80 for sure, for good color quality. But a high CRI in itself doesn't imply good color rendition. It gets pretty complex, which for the purpose of this article isn't important. The bottom line is to have a CRI above 80 for better color rendering of people and things in general.
Some CFL manufacturers label their bulbs with a 3 digit code to specify their CRI and color temperature. The 1st digit represent the CRI measured in tens of percent, while the second 2 digits represent the color temperature measured in hundreds of Kelvins. For example, a CFL with a CRI of 84 and a color temperature of 2800K would be given a code of 828.
This is what decorators really pay attention to. The early CFLs had a low CRI value, but today you can buy CFLs with higher CRI values, even in the daylight range. Avoiding CFL lighting in your hotel because you want color to be "true" is costing you lots of money. You can have your energy conserving CFLs and accurate color rendition. And as LED bulbs get better you can save even more money with your energy bill.
A lumen is a unit of light measurement. It's the total quantity of light emitted by a bulb or how much light is present. Simply stated, the more lumens the more light. More watts doesn't necessarily mean more light, but watts per lumen is an efficacy measure of the bulb.
ambient lighting: 400-800 lumens
general room lighting: 800-1700 lumens
reading: 1700-2800 lumens
You may see the term lux, which is the abbreviation for lumens per square meter. 1000 lumens lighting a one square meter area is referred to as 1000 lux. And if that same 1000 lumens lit 10 square meters the reference is 100 lux. The larger the area you want lit the more lumens you need.
So now you know some of the terminology you'll possibly see on light bulb packaging. I'll discuss how it fits together in the sequel to this article, Using Energy Efficient Light Bulbs.
Posted by Kit