Confused about buying new light bulbs now that many of the old tried and true (and inexpensive) incandescents are banned? If so, you are not alone.

Last week, we explained how to locate—and understand—the light output of an LED lamp, as identified on the mandatory FTC label of the light bulb box. As you probably noticed when looking at all the new light bulbs on the store shelves, the traditionally used label, “Watts”, is no longer used to identify brightness, as it cannot adequately identify light output for new energy-efficient lamps. If you missed that blog, you can read it here: How to replace your phased-out (banned) light bulb with LED light bulbs: Understanding the label on the box.

“Brightness”, however, isn’t the only non-traditional term used on the FTC label of these new energy-efficient light bulbs: Color quality (measured by the Color Rendering Index), Power Factor (measured by a dimensionless number between -1 and 1, but often displayed as a percent), and Light Appearance (measured in degrees Kelvin) are used as well. So this week, we’ll take a closer look at each of these non-traditional light bulb descriptors.

CRI

CRI stands for Color Rendering Index and is the standard criteria used to evaluate light quality. It sets out to determine how well the light bulb can reproduce the colors of various objects dependably. Most of us have experienced buying clothing in a store only to return home to find out it’s a different color than we initially thought. This has to do with the light source and how it ranks in CRI. CRI, therefore, allows you to determine how faithfully colors are represented under your light source. It’s an incredibly important metric in determining light quality.

CRI averages 8 colors (which have a low to medium chromatic saturation) to obtain a ranking between 0 and 100.

Image: Color Rendering Index color palette

Sunlight has a very broad, even spectrum, so it’s considered ideal and is defined to be 100 CRI. Fluorescents, on the other hand, typically rate around 70, although some speciality fluorescent lamps can achieve CRI ratings in the 90s. Because they are basically brightly glowing heat sources, halogen and incandescent lamps mimic the sun and carry the highest CRI rating among artificial light sources at approximately 97 to 100. So where do LEDs fall on the CRI? Due to the lack of LED manufacturing standards and a still-young technology, the CRI value of LEDs can range between less than 70 and over 90. This is why it is important to be able to make the distinction between a good quality LED bulb and a bad one.

Note: At Leapfrog Lighting, our regular CRI light bulbs test at 83-85 CRI, while our high CRI lamps test at 95-97 CRI. Check out our datasheets for more information.

Extra: The limitations of CRI as a measurement system are well known in lighting circles, but it is still the recognized and accepted method. There is an entire faction lobbying to do away with CRI in favor of the Color Quality Scale (CQS), which was developed by the National Institute of Standards and Technology (NIST). For more information about how CQS differs from CRI, see Attention CRI: You’re no longer relevant.

Power Factor

Power Factor is a measure of how well a lamp absorbs the power it’s supplied (ie. “the ratio of real power flowing to the load to the apparent power in the circuit”*), and is a dimensionless number between -1 and 1. It is measured by determining the number of Watts and dividing it by the measured voltage and current. In light bulbs, a low power factor draws more current than a high power factor to produce an equivalent amount of light. That is to say, low power factors lose more power in the form of heat. Accordingly, for all electrical products that operate from the AC power grid (like light bulbs), the higher the power factor, the greater the energy efficiency. The power factor of Leapfrog’s LED light bulbs is .97, often expressed on the FTC label in percentage form (ie. 97% efficient). Compare this to many LED light bulbs that waste as much as 30% of the energy they draw.

*Wikipedia

Light Appearance

Light appearance, also known as color temperature, identifies the color of the light emitted by the light bulb. It is measured numerically on the degrees Kelvin (K) scale. In terms of light bulbs, the Kelvin temperature allows manufacturers to categorize their products as warm (~2700K), neutral (~3000K), or cool (~5000K). This is why you will often see marketing language such as “warm white” to describe an LED light bulb around 2700K.

Extra: The science behind determining color temperature values is based on the principle of the black body radiator. As the black metal starts to heat, the metal turns red-yellow. As it gets hotter it starts to turn white before getting even hotter and turning blue. In lighting, the color of the light emitted by the light bulb is matched to the color of the heated black metal at that specific degrees Kelvin. If it’s white light emitted from the light bulb has a hint of red-yellow, the heat of the black metal is probably around 2700K.

In a nutshell, the lower the degrees Kelvin, the warmer or yellower the light appearance (the traditional incandescent light bulb is warm at 2700K). The higher the degrees Kelvin, the cooler or whiter the light appearance (the traditional office and hospital lighting is cool at 5000K).

The FTC label requires a light appearance scale to indicate the color temperature of a light bulb. For example:

Image: Leapfrog Lighting PAR30 Lighting Facts label

The handy color temperature chart below is very helpful at matching light bulb color temperature with known quantities, such as candle light and direct sunlight (the color temperatures in blue text represent the most common color temperatures of LED lamps). The light bulb itself produces a white light, but is tinged with the colors of the spectrum below.

Source: www.LeapfrogLighting.com

Fact: Not only does the lighting application determine the correct color temperature to use (ie. grocery store, operating room, living room), but people also have strong preferences based on their geographical location. At Leapfrog Lighting, we’ve observed in North America that the most northern states and Canada prefer a warmer color temperature, while the most southern states prefer a cooler temperature. This preference can be said to be dictated by the amount of sunlight experienced in a given region.

Now that you can understand the light bulb box of energy-efficient LED light bulbs, you are well armed to select the best LED light bulb to replace your banned incandescent.  Good luck!