Full spectrum light bulbs are any of a number of bulbs that produce light that absorbs the full range of colors, and in most cases are designed to emulate sunlight. There is no precise scientific definition for “full spectrum” in this context and it is generally understood to be a marketing term. As such, there can be a great deal of variation when it comes to what, exactly, a bulb carrying this label will deliver. They are popular choices for people with seasonal depression and their brightness and ability to illuminate colors also makes them useful for people who suffer from eyestrain or who need to focus on intricate details, like words on a screen or stitches in a sewing project.
Origins of the Term
The term “full spectrum” was essentially made up by light bulb companies as a way to distinguish products that illuminate all colors from bulbs with a more limited range, like “soft white” or “cool white.” They are called this because, in most cases, they are designed to highlight and intensify colors across the spectrum from neutral to warm to cool, much as the sun does. These sorts of bulbs might also be called “daylight” or “natural light,” depending on the market.
Placement on the Color Rendering Index
One of the most important features of this sort of bulb is its placement on the Color Rendering Index (CRI). The CRI is a measure used by the lighting industry to indicate a bulb's ability to render colors in objects, and different measurements are why some objects look brighter in different types of lighting. Bulbs with an index rating of 90 to 100 are generally the best at simulating the quality of light produced by the sun. There isn’t usually any sort of industry regulation requiring that bulbs labeled “full spectrum” fall within this range, but as a general rule most do.
Importance of Color Temperature
The temperature of the light emitted also factors in. In this instance, “temperature” doesn’t mean how hot the bulb gets, but rather corresponds to the relative intensity of the light emitted. A light source's color temperature describes the color of the light. In general, bulbs with color temperatures of 5000 Kelvin (K) or more produce light that is similar to daytime sunlight.
Standard incandescent bulbs coated with neodymium are a notable exception. These are sometimes marketed under the “full spectrum” name, although they do not usually have a 5000K color temperature. They are usually able to filter out the harsh yellow tint that is common in standard incandescent bulbs, however, which makes them more desirable in many settings.
Full spectrum light bulbs are available in many different sizes, styles, and qualities. There also tends to be a certain amount of variance even within styles. Since there is no standardized definition of what it means to be “full spectrum,” it’s often possible to find bulbs that emit fairly different light all labeled with this common terminology.
Part of the difference may be owing to the sun itself. The sun’s light changes based on atmospheric conditions, time of day, and geospatial location, and it’s all but impossible for a light bulb to reflect this sort of regular change. Manufacturers generally pick one slice of the spectrum on which to focus. Some are broader than others, and some brighter. All have the same general goal of illuminating more than other standardized bulb types, though.
People often choose full spectrum bulbs for use in craft rooms, in lamps used to help see stitching, and in any other context where color and precise illumination are important. This sort of light is also known to reduce eyestrain and screen glare, making is popular for people who spend a lot of time typing or looking at screens. Using these sorts of bulbs in offices, particularly those without many windows, can also help improve mood and brighten spaces that might otherwise feel gloomy. Full spectrum light bulbs are said to not only improve mood, but also energy, learning ability, and behavior.
They are also a popular choice for people who suffer from Seasonal Affective Disorder (SAD), also known as seasonal depression. Many healthcare experts recommend that SAD patients spend a portion of each day in front of a light that mimics sunlight in order to bring their circadian rhythms and hormonal balances back to normal. Not all full spectrum lights are beneficial in this context. Bulbs usually need to emit at least some ultraviolet, or UV, rays in order to be effective; specially designed SAD lamps do, but this isn’t usually true of every bulb in the full spectrum family. Most full spectrum options mimic sunlight in color, but not necessarily in intensity, UV emission, or vitamin absorption.