While the definition of a full spectrum lamp may vary, most would at least agree it is a lamp that displays light at all wavelengths of the visible spectrum, and perhaps some invisible light. The purpose of this is to better simulate natural lighting conditions, which may offer a number of benefits. A full spectrum lamp does this by using special full spectrum bulbs that vary greatly from traditional incandescents and fluorescents.
The health benefits of full spectrum lighting have been touted for years. It is thought to help seasonal affective disorder, which many people at higher latitudes may suffer from in the winter. It is also thought to regulate body functions better and even promote plant growth. The theory behind this is relatively simple -- all living organisms have been especially designed to work under lighting conditions the sun produces. Therefore, imitating these conditions artificially should provide some benefit. That is what a full spectrum lamp seeks to do.
Full spectrum lamps are not necessarily cheap. Even a low-end lamp can costs as much as $30 US Dollars (USD), just for one. This compares with $10 USD or less for a comparable desk lamp. Of course, the biggest cost is in the price of the full spectrum light bulbs. A 40-watt, full spectrum bulb will cost nearly triple or quadruple what a similar wattage, traditional incandescent will cost. In most cases, it may be more cost efficient to buy a traditional lamp, and simply replace the included bulb with a full spectrum bulb, which are designed to fit most standard light fixtures.
While a full spectrum lamp may claim to be energy efficient, it should be noted that not all of them are. Further, because the energy efficiency of a full spectrum lamp is usually a secondary consideration, there are other products on the market that tend to be a lot more energy efficient. Therefore, this is not necessarily the sole reason on which to base a purpose for a full-spectrum lamp.
Some studies claim that the benefits of a full spectrum lamp are overstated. For example, full spectrum light was shown to exhibit no better benefits than traditional artificial light sources when it came to helping with seasonal affective disorder, according to the Lighting Research Institute, a division of the Rensselaer Polytechnic Institute in Troy, New York. Further, health benefits associated with some forms of UV light can be obtained without the use of a full spectrum lamp.
Despite this, the popularity of full spectrum lighting is hard to ignore. Whether or not there are health benefits, most do agree it tends to display colors in a more natural way. Fluorescents, and to a smaller degree incandescents, tend to cast a yellowish hue on surfaces. This is especially easy to see in some photographs where a proper white balance is not set, making the camera lens more sensitive to yellow light.