Lightning is one of nature’s most awe-inspiring sights. The flash of brilliant white lightning across a dark sky is beautiful, powerful and sometimes dangerous. But have you ever noticed that lightning isn’t always white? Sometimes it can appear blue, violet or even pink. So what causes these different colored lightning bolts? And is lightning ever truly blue?
What Causes Lightning?
To understand what causes the different colors of lightning, we first need to understand what causes lightning in general. Lightning is a massive electrostatic discharge that occurs between electrically charged regions within clouds or between a cloud and the ground. These discharges are massive—a single bolt of lightning can contain over a billion volts of electricity!
Lightning forms when colliding ice particles within a cloud cause a separation of electrical charges. Positively charged ice crystals rise to the top of the cloud while negatively charged ice particles sink to the bottom. This separation of charge creates tremendous electrical potential energy. When this electrical potential becomes too great, the insulating properties of the air break down and a lightning bolt streaks across the sky as the two oppositely charged regions rapidly discharge.
What Causes the Color of Lightning?
The color of lightning is primarily determined by the temperature of the bolt. All lightning starts out as an extremely hot, bright white arc of plasma. But as this bolt travels through the atmosphere, interactions with air molecules cool the plasma arc down, changing its visible light emissions and apparent color.
Cooler lightning bolts appear more red or orange, while hotter lightning remains white or shifts toward the blue end of the spectrum. Interestingly, taller lightning bolts are generally hotter and bluer since they stretch up higher into the atmosphere before cooling down significantly. Meanwhile, shorter bolts tend to be cooler and more reddish in color.
Factors That Influence Lightning Color
Several factors can influence the temperature and color of a lightning bolt:
- Atmospheric impurities – Dust, pollution, water droplets and other particles interact with the plasma arc, accelerating its cooling.
- Altitude – The higher a bolt travels through the atmosphere, the less it cools before striking the ground.
- Distance – Distant lightning appears more red as the longer path length promotes cooling.
- Intensity – More intense lightning tends to be hotter and bluer.
- Branching – Branched lightning cools and spreads the current, shifting colors toward the red end of the spectrum.
Is Lightning Ever Truly Blue?
So this brings us back to the original question: Is lightning ever truly blue? Or are our eyes just being deceived into seeing blue when lightning is in fact white or violet?
The answer is that lightning can indeed emit blue light, though it is rare. Here’s a look at the electromagnetic spectrum of lightning:
| Color | Wavelength |
|---|---|
| Red | 700-635 nm |
| Orange | 635-590 nm |
| Yellow | 590-565 nm |
| Green | 565-500 nm |
| Blue | 500-450 nm |
| Violet | 450-400 nm |
Lightning does produce some light in the blue wavelength range, though the majority of emissions are at shorter, violet wavelengths. Our eyes perceive these violet emissions as a light blue or purplish-white color. Truly blue lightning independent of violet emissions is possible but rare.
When Lightning Appears Blue
There are a few specific scenarios that can result in lightning appearing blue to our eyes:
- Distant lightning – As lightning travels longer distances, the shorter wavelength violet emissions get scattered away by air molecules, leaving mostly longer wavelength blue light to reach our eyes.
- High altitude lightning – Some types of lightning like sprites and jets occur at the edge of space, above most of the atmosphere. With less cooling, these bolts retain more blue and violet emissions.
- Positive lightning – About 5% of lightning strokes are positively charged. These hotter bolts tend to be bluer and contain more blue emissions.
So while lightning is usually white or violet, blue lightning is possible under the right circumstances. The next time you see a dramatic blue flash light up the sky, it just might be real blue lightning!
Lightning Safety Tips
While beautiful, lightning can also be extremely dangerous. Follow these tips to stay safe if lightning is nearby:
- Seek shelter in a building or vehicle, avoiding open fields, high ground and isolated trees.
- Unplug electrical devices and avoid using landline phones.
- Wait at least 30 minutes after the last observed flash before resuming outdoor activities.
- If caught outside during lightning, crouch down into a ball but avoid laying flat on the ground.
- If someone is struck by lightning, call 911 and begin CPR if needed.
The Color and Science of Lightning
Lightning remains an awe-inspiring force of nature. The colors of lightning adds to its mystery and beauty. With a mix of violet, blue and white emissions, lightning continues to fill our skies with brilliant flashes of color and light.
