Common Incandescent Light Bulb
The most common type of lighting source used is the incandescent light bulb. However, it's also one of the least efficient. It works by passing electricity through a metal filament, generating heat. Once the temperature reaches around 500 degrees C (943 degrees F), the filament starts emitting light along with heat. The light produced is adequate for illumination, but it significantly differs from natural sunlight. This is because most of the energy consumed by incandescent bulbs is wasted on producing infrared radiation (heat), with only about six percent of the energy input being used to produce light. As a result, the light emitted tends to be rich in red and its neighboring hues, while having minimal violet, blue, and green.
Fluorescent Strip Lighting
Fluorescent strip lighting is commonly used in offices and factories and is more energy-efficient. It operates by creating ultraviolet rays within a glass tube through a mercury vapor arc. The inner surface of the tube is coated with special luminescent compounds that, when exposed to the ultraviolet rays, emit light in specific colors. The colors emitted depend on the types of compounds used. Generally, these tubes are designed to produce a high level of yellow-green light, which corresponds to the colors most sensitive to the eye. Despite offering a seemingly bright light while consuming relatively little energy, the light from fluorescent strips remains notably different from natural sunlight.
Full Spectrum Lighting
Full spectrum lighting replicates the spectral balance of natural daylight, emitting ultraviolet light and all colors in the spectrum from red to violet. These lights are particularly beneficial for light therapy in the treatment of Seasonal Affective Disorder (SAD).
Full spectrum lighting closely resembles fluorescent tubes in its design, utilizing a mercury vapor lamp to produce ultraviolet light. The tube's surface is coated with a compound designed to emit the full spectrum of colors when exposed to the ultraviolet light. This coating aims to mimic the spectrum found in natural sunlight, excluding harmful ultraviolet rays. Typically, protective shields are provided to prevent users from accidental exposure to ultraviolet light.
Full Spectrum Lighting vs. Broad Spectrum Lighting
Full spectrum light bulbs aim to replicate natural sunlight, which includes ultraviolet rays. They generally have a high Color Rendering Index (C.R.I.) of 90 or above (outdoor light has a CRI of 100) and a kelvin temperature of 5,000 or higher. Full spectrum light is often described as having a purplish or bluish cast. Many light box companies now include UV ray blocking in their diffuser screens, so ensure this feature when purchasing their products.
Broad spectrum light boxes are often considered similar to full spectrum but without the UV rays. Typically, they have a CRI of around 82 and a kelvin temperature of approximately 4,200. Broad spectrum light bulbs provide a pure white light without the risk of UV exposure.
Ultraviolet Light
One of the primary safety concerns regarding light therapy is the potential exposure to ultraviolet (UV) light. UV light exposure can result in sunburn, damage to the eyes, and skin cancer. Recent studies have demonstrated that UV rays are not necessary for effective light therapy; units that emit minimal UV light can still be highly effective. Many light box manufacturers provide shields to filter out UV light, so ensure that the unit you purchase complies with this safety feature.