In contrast, ultraviolet (UV) “light” is high-energy radiation that is invisible. Because of the non-visible nature of UV, many eye care professionals and scientists avoid using the term “UV light,” and prefer “UV radiation” instead.
The energy of electromagnetic radiation (including UV and HEV) is inversely related to its wavelength. Rays with shorter wavelengths have higher energy; those with longer wavelengths have lower energy.
UV radiation has shorter wavelengths and therefore more energy than visible light. The portion of the visible light spectrum that is closest to the UV band comprises violet and blue light rays.
Because these rays have shorter wavelengths and higher energy than other visible light, they are classified as “high-energy visible” (HEV) light.
There is some disagreement regarding the exact boundary between UVA radiation (the segment of the UV spectrum with the longest wavelengths) and HEV light. Most sources, however, say this occurs at a wavelength of 380 nanometers (nm), creating these categories:
UVA: invisible electromagnetic rays with wavelengths ranging from 315 to 380 nm.
HEV: visible light rays with wavelengths ranging from 380 to 500 nm.
Some sources place the cut-off between UVA and HEV light at 400 nm. If this criterion is used, the definitions change to:
UVA: invisible rays with wavelengths ranging from 315 to 400 nm.
HEV: visible light rays with wavelengths ranging from 400 to 500 nm
The entire UV spectrum has wavelengths ranging from 100 nm to 380-400 nm. Visible light has wavelengths ranging from 380-400 nm to approximately 700 nm.
SOURCES OF HEV LIGHT
The primary source of HEV light outdoors is the sun. An estimated 25 to 30 percent of sunlight consists of HEV light rays.
The primary sources of HEV light indoors include:
• Residential and commercial lighting
• Desktop computer screens
• Laptop computer screens
• Tablet computer and e-reader screens
• Smart phone screens
Residential and commercial lighting includes LED light bulbs, compact fluorescent light (CFL) bulbs, halogen light bulbs, fluorescent tubes and incandescent light bulbs. Of these, LED bulbs emit the highest amount of HEV rays (about 10 percent of total light output), followed by CFL bulbs. Incandescent light bulbs typically emit less than 5 percent HEV light.
The amount of HEV emitted by computers and portable electronic devices may be relatively small, but users look directly at these light sources at close range, which may increase eye risks. Still, it’s important to keep blue light exposure from man-made sources —including portable electronic devices —in perspective. The following table shows the HEV exposure from these sources relative to that from natural sunlight.
From this data, it’s apparent that a person spending their entire day indoors using a computer and other electronic devices will still have significantly less HEV exposure than a person spending a nominal amount of time in natural sunlight outdoors without protective sunglasses.