📚 The Electromagnetic Spectrum: The Science of 625 nm Red Light | 电磁波谱：625纳米红光的科学
The electromagnetic spectrum is the complete range of electromagnetic radiation, from low-energy radio waves to high-energy gamma rays. Visible light occupies only a narrow window in this spectrum, and 625 nm is a wavelength we recognise as red light.
电磁波谱是电磁辐射的完整范围，从低能量的无线电波到高能量的伽马射线。可见光仅占据这一波谱中狭窄的一段，而625纳米是我们识别为红光的波长。
1. What Is Electromagnetic Radiation? | 什么是电磁辐射？
Electromagnetic (EM) radiation is a form of energy that travels as transverse waves. It consists of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of travel.
电磁（EM）辐射是以横波形式传播的一种能量。它由相互垂直且与传播方向垂直的振荡电场和磁场组成。
EM waves can travel through a vacuum at the speed of light, c = 3 × 10⁸ m/s. They require no medium, unlike sound waves.
电磁波可以在真空中以光速 c = 3 × 10⁸ m/s 传播。与声波不同，它们不需要介质。
2. Wave Properties: Wavelength, Frequency and Energy | 波的性质：波长、频率与能量
Wavelength (λ) is the distance between two consecutive peaks or troughs of a wave. Frequency (f) is the number of waves passing a point per second, measured in hertz (Hz).
波长（λ）是波的两个相邻波峰或波谷之间的距离。频率（f）是每秒通过某一点的波的个数，单位为赫兹（Hz）。
The wave speed is related to wavelength and frequency by the equation:
波速与波长和频率的关系由以下方程给出：
c = f × λ
For light in a vacuum, c is constant. Therefore, a longer wavelength means a lower frequency, and vice versa.
对于真空中的光，c是常数。因此，波长越长，频率越低；反之亦然。
The energy of a single photon is given by E = h × f, where h is Planck’s constant (6.63 × 10⁻³⁴ J·s). Higher frequency means higher energy.
单个光子的能量由 E = h × f 给出，其中h是普朗克常数（6.63 × 10⁻³⁴ J·s）。频率越高，能量越大。
3. The Visible Spectrum: Where Does 625 nm Fit? | 可见光谱：625纳米位于哪里？
The visible spectrum ranges from about 380 nm (violet) to 750 nm (red). Each colour corresponds to a specific range of wavelengths.
可见光谱范围大约从380纳米（紫色）到750纳米（红色）。每种颜色对应特定的波长范围。
The table below lists common visible colours and their approximate wavelength ranges.
下表列出了常见可见光颜色及其大致波长范围。
| Colour / 颜色 | Wavelength range (nm) / 波长范围（纳米） |
|---|---|
| Red / 红 | 620–750 |
| Orange / 橙 | 590–620 |
| Yellow / 黄 | 570–590 |
| Green / 绿 | 495–570 |
| Blue / 蓝 | 450–495 |
| Violet / 紫 | 380–450 |
625 nm lies in the red region, close to orange. It is commonly used in red lasers and LED display lights.
625纳米位于红色区域，靠近橙色。它通常用于红色激光和LED显示屏灯。
4. How We Perceive Red Light | 我们如何感知红光
The human retina contains two types of photoreceptor cells: rods and cones. Cones are responsible for colour vision and work best in bright light.
人类视网膜包含两种感光细胞：视杆细胞和视锥细胞。视锥细胞负责颜色视觉，在明亮光线下工作最佳。
There are three types of cones with different spectral sensitivities. The long-wavelength cones (L-cones) are most sensitive to red light around 560–580 nm, but they still respond strongly to 625 nm. This is why 625 nm appears bright red.
有三种类型的视锥细胞，具有不同的光谱敏感度。长波视锥细胞（L-视锥）对约560–580纳米的红光最敏感，但对625纳米也有强烈响应。这就是为什么625纳米看起来是亮红色。
5. Applications of 625 nm Red Light | 625纳米红光应用
Red light at 625 nm has several practical uses.
625纳米红光有几种实际用途。
- Barcode scanners / 条形码扫描器: Helium-neon lasers and laser diodes around 632.8 nm are used to read barcodes.
- Laser pointers / 激光笔: Many handheld pointers emit at around 635–650 nm.
- LED displays / LED显示屏: Red LEDs with peak wavelengths near 625 nm are used in screens and signage.
- Optical communication / 光通信: Plastic optical fibres use red laser light for data transmission.
- Red light therapy / 红光疗法: Low-level red light is used in medicine to stimulate cell repair and reduce inflammation.
Note that the exact wavelength may vary, but all these devices rely on the principle of photon emission by electrons transitioning between energy levels.
注意精确波长可能有所不同，但这些设备都依赖于电子在不同能级间跃迁发射光子的原理。
6. The Wider Electromagnetic Spectrum | 更广阔的电磁波谱
The EM spectrum is arranged by increasing frequency and decreasing wavelength.
电磁波谱按频率递增、波长递减排列。
Starting from the lowest frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
从最低频率开始：无线电波、微波、红外线、可见光、紫外线、X射线和伽马射线。
The table below gives typical wavelengths and uses for each region.
下表给出了每个波段的典型波长和用途。
| Region / 波段 | Typical wavelength / 典型波长 | Use / 用途 |
|---|---|---|
| Radio / 无线电波 | > 0.1 m | Broadcasting / 广播 |
| Microwave / 微波 | 1 mm – 0.1 m | Cooking, radar / 烹饪、雷达 |
| Infrared / 红外线 | 700 nm – 1 mm | Remote controls, night vision / 遥控器、夜视 |
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