Lasers have become an integral part of our daily lives. From scanning barcodes at the grocery store, to laser eye surgery, to laser light shows, lasers play many important roles in the modern world. Two of the most common laser colors are purple and blue. But which one is better? In this article, we’ll examine the pros and cons of purple vs. blue lasers.
How Lasers Work
First, let’s do a quick overview of how lasers work. Lasers are devices that generate an intense beam of coherent light, all at one wavelength. This wavelength determines the laser’s color. Purple lasers typically have a wavelength of around 405-450nm, while blue lasers are around 473-491nm.
Within the laser device, energy from electricity or light is used to excite electrons within atoms. When the electrons fall back down to their normal state, photons are released. Between two mirrors, these photons bounce back and forth, causing more photons to be released in the same direction with the same wavelength and phase. One mirror is half-silvered, allowing some of the photons to escape as the laser beam.
Power and Brightness
An important consideration when choosing a laser color is the power and brightness. More power means a brighter beam and the ability to pop balloons or light matches from farther away.
On average, blue lasers tend to be brighter than purple lasers. Blue lasers using GaN or InGaN semiconductors can achieve optical powers of up to 500 mW, while most purple lasers top out around 200 mW.
Higher power also usually means better coherence and focus for the laser beam. So for applications where brightness and intensity are critical, such as laser light shows, blue tends to work better than purple.
Cost
Another key factor is cost. In general, blue lasers are more expensive than equivalent purple lasers. Here are some typical prices for low power laser pointers:
| Laser Color | Price |
|---|---|
| Purple | $3 – $20 |
| Blue | $5 – $50 |
This price difference is largely due to manufacturing costs. The GaN semiconductors used in blue lasers are more expensive to produce than the diodes used in most purple lasers. The additional research and development costs also drive up the price of blue lasers.
Safety
Laser safety is also an important consideration. Both purple and blue lasers are extremely dangerous if shined directly into the eye. However, blue lasers present a higher risk because of the shorter wavelength.
The high photon energy of blue light causes more damage to the retina than lower energy purple light. Staring into a blue laser is more likely to permanently damage vision after even a brief exposure. Blue laser light also penetrates deeper into eye tissue before becoming absorbed.
For these reasons, blue lasers above 5 mW are classified in the highest danger Class IV category, while purple lasers don’t reach this category until power exceeds 30 mW. So purple lasers have a better safety profile overall.
Applications
The best laser color also depends on the application. Here are some examples where one color works better than the other:
- Reading CD/DVD/Blu-Ray discs – Blue lasers are required for Blu-Ray discs. Purple works for CD/DVD.
- Laser light shows – Blue is brighter and works better for longer distance shows.
- Water shows – Purple stands out better when scattering in water vapor or fog screens.
- Astronomy pointing – Purple is easier to see and track against the night sky.
- Photochemical reactions – Blue light has the right wavelength to activate some chemical bonds.
So consider the intended use before choosing between purple and blue lasers.
Conclusion
To summarize the key differences:
- Blue lasers are brighter and more powerful.
- Purple lasers are more affordable.
- Blue laser light is more hazardous to eyesight.
- Certain applications like Blu-Ray discs require blue lasers.
- Other applications like water shows use purple better.
In the end, there is no definitive “better” between these two popular laser colors. The needs of the specific application should determine whether purple or blue is the right laser choice.
Power and coherence are the key advantages of blue lasers. But for general laser pointing and experiments, the lower cost and improved safety of purple lasers make them a great option. If brightness isn’t essential, but you still want an impressive laser beam, purple is likely the better choice for most uses.
