Blacklights can be cool! And also at times practical during CSI-style investigations. Whatever a blacklight shines on, it glows in radiant fluorescent colors. But can this really be safe for our eyes?
Blacklights emit ultraviolet light. UV light can be damaging to the eyes and cause a condition called photokeratitis or sunburned eyes. However, the long wavelengths of UV light that blacklight output are unlikely to cause any significant damage with normal routine use.
If you are going to have extended exposure to blacklights, it can be helpful to protect your eyes. But to understand the most about this ultraviolet light exposure, we first have to learn more about how blacklights work.
How Black Lights Work
Light (or more accurately called electromagnetic radiation) exists in a spectrum. There is light that we can see, visible light, and light that is outside of the range of what we can see. This includes longer wavelengths such as infrared, radio waves and microwaves and shorter wavelengths such as ultraviolet waves and x-rays.
Electromagnetic spectrum of light; image by Philip Ronan, CC BY-SA 3.0, via Wikimedia Commons
Normal lights output visible light (this is the reason we use normal lights). But these lights also can produce light or radiation outside of the visible light spectrum.
Some light bulbs, such as incandescent lights, will output a considerable about of infrared light with a very small level of ultraviolet light.
Other lights such as fluorescent lights are different. These lights work by passing electricity through a tube of mercury and an inert gas. This electricity causes the mercury to give off ultraviolet light.
But the good news is this much of this ultraviolet light doesn't make it out of the light-bulb. A fluorescent light is coated with something called a phosphor. When phosphors’ absorb radiation, they output radiation at a longer wavelength. What this means is that the coating of a fluorescent light absorbs UV light and outputs the white visible light that we see.
Blacklights are simply just a modified form of fluorescent lights. Instead of emitting white visible light, the phosphor coating of blacklights absorb ultraviolet light and output a longer form of ultraviolet light. The shorter (and more harmful) types of UV light, UVC and UVB, are blocked and longer (and less harmful) variety, UVA is given off. The black coating of blacklights blocks most visible light except for the violet and some blue that we see when we look at a black light.
Blacklights can also be made from incandescent lights with a black filter to block the visible light from the light bulb.
So what do we have? We have a light designed to produce longer ultraviolet waves.
What's the purpose of blacklights?
Blacklights do have useful purposes outside of just fun and novelty. Phosphors, the same things used to coat the light, exist pretty much everywhere. When shining a blacklight on these phosphors, these phosphors absorb the UV light and give off visible light; in essence, they glow!
Phosphors in our detergent causes our clothes to glow under a blacklight. Phosphors added to paint can cause colors to vibrantly fluoresce.
But phosphors are also used in more useful situations such as detecting counterfeit money or antiques, evaluating air conditioner leaks or in crime scene investigations.
Blacklight evaluating money; image by Scott Nazelrod, Public domain, via Wikimedia Commons
Concern About UV Light
Ultraviolet light can be damaging not only to our skin but also to our eyes. Excess exposure to UV light can cause you to develop something known as photokeratitis or sunburned eyes.
Photokeratitis causes short-term damage to the “skin" on the surface of our eye, called epithelium. When exposed to UV light, these cells can become damaged and die off. Fortunately, just as our skin will recover after a sun burn, our eyes will recover as well. This epithelium is constantly being produced and new cells will replace the old ones.
But in the meantime, the eyes can feel uncomfortable or painful. You may notice:
- Burning or Scratchiness
- Light Sensitivity
- Watery Eyes
- Blurry vision
These are all symptoms that your cornea has experienced damage from ultraviolet light. And you may feel these symptoms for a few days until the cornea has fully healed back over.
Back to Blacklights
Not all UV light is created equal. The shorter the wavelength of UV light, the more it is absorbed by the cornea (and thus the more damage it does).
This is important when we look at blacklights. Blacklights only emit the longer form of ultraviolet light, UVA light. In addition, the UV light from blacklights is even on the long end of the spectrum of UVA light. The wavelength puts it close to visible light.
This is contrast to other sources of UV light (such as a tanning bed), which have a greater range including shorter wavelengths of UV light.
So what does this all mean? Blacklights, while a source of ultraviolet light, aren't as harmful as other sources of UV light such as the sun, welding or in a tanning bed.
From normal exposures to blacklights, there is a low chance that you can develop photokeratitis or sunburned eyes. Especially if you aren't staring directly at the blacklight bulb. You are more likely to develop photokeratitis just by being outside in the sun without sunglasses.
Protect Yourself From Blacklights
But how can you protect your eyes from blacklights if you are going to have prolonged exposure? The best way is to wear glasses which block UV light. These glasses will filter out the harmful UV rays to avoid over exposing your eyes to UV light. When evaluating glasses, you will want to make sure that the glasses block out 99-100% of UV light. Safety glasses can come with UV protection (on a scale with U6 being the most protection) or you can also look to UV400 rated sunglasses.
Summary
Blacklights can be a source of UV radiation. But blacklights emit a high wavelength of UV light which is less damaging to our eyes. Normal exposure to blacklight is unlikely to cause any significant damage to your eyes. But since ultraviolet light still can damage eyes, it is beneficial to wear UV protection when expected to have prolonged exposure to blacklights.
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