Of course! This is an excellent question that touches on physics, engineering, and human biology. The pulsating effect you observed is a combination of how the light is generated and how your eyes perceive it.

Here is a breakdown of your questions:

1. Why do LEDs and artificial lights flicker or pulsate?

Yes, many artificial lights flicker, but it's usually too fast for us to consciously perceive. This flicker is a byproduct of how they are powered.

• AC Power: Most homes use Alternating Current (AC) power, which reverses direction 50 or 60 times per second (50Hz or 60Hz). This means the power supplied to the bulb effectively turns on and off 100 or 120 times per second.
• LEDs and Drivers: LEDs are diodes, meaning they only allow current to flow in one direction. A simple LED circuit on AC power would only light up half the time. To solve this, LEDs use a component called a driver.
  • Low-quality drivers may not fully smooth out the AC power, causing the LED to dim and brighten 100/120 times a second. This is the "flicker."
  • High-quality drivers use capacitors to store and release energy, smoothing out the power delivery and creating a much more constant light with minimal flicker.
• Dimming (PWM): Many dimmable LEDs use a technique called Pulse Width Modulation (PWM). Instead of reducing voltage, the driver turns the LED on and off thousands of times per second. The shorter the "on" time, the dimmer the light appears.

Is it visible? For most people, flicker above ~80Hz is not consciously visible due to persistence of vision. However, our brains still process it, and it can sometimes lead to eye strain, headaches, or a general sense of unease. You can often see this flicker by:

• Viewing the light through your phone's camera (especially in slow-motion mode).
• Waving your hand or a pen quickly in front of the light, creating a "strobe" or "phantom array" effect.

2. Does the Sun actually pulsate?

Yes, the Sun does pulsate, but not in any way that is perceptible to the human eye.

The Sun is a dynamic ball of plasma with complex processes happening inside. The study of its oscillations is called helioseismology.

• Solar Oscillations: The Sun "rings" like a giant bell due to pressure waves (sound waves) reverberating through it. These cause the surface to move up and down by several hundred meters over periods of about five minutes.
• Light Output Variation: These oscillations cause minuscule variations in the Sun's brightness. Additionally, the Sun's total output varies by about 0.1% over its 11-year sunspot cycle.

Is it perceptible? Absolutely not. These variations are incredibly small and slow, requiring highly sensitive scientific instruments to detect. The "twinkling" we see from stars (and the Sun, if you could look safely) is caused by atmospheric scintillation, where turbulence in Earth's atmosphere distorts the light path, not by the star itself pulsating.

3. Do all light sources have some form of pulsation?

No, not all light sources pulsate in the same way. The constancy of a light source depends on its power source and mechanism.

So, a light source powered by a battery (DC) is about as close to a truly constant light source as you can get.

4. What causes the visual perception of pulsation or halos?

This is the most likely explanation for what you personally observed: the "pulsation with light radiating outward." This is almost certainly an effect of your eyes and brain, not the light source itself.

Here are the primary causes:

• Tear Film Instability: The most common cause. Your cornea is covered by a thin layer of tears. This film is not perfectly smooth and is constantly shifting, evaporating, and being replenished when you blink. As it moves, it slightly refracts the light entering your eye, causing bright points of light to appear to shimmer, pulse, or send out rays.
• Diffraction: Light waves bend (diffract) as they pass through a small opening—in this case, your pupil. This creates a faint pattern of rings and lines around a point source of light, known as an Airy disk. Small changes in your pupil size can alter this pattern, contributing to a sense of movement.
• Imperfections in the Eye: No one's eye is optically perfect. Tiny imperfections in the cornea or lens can scatter light, creating effects like halos (rings) or starbursts (rays). These can seem to shift or pulse as your eye makes tiny, involuntary movements (saccades).
• Floaters: The vitreous humor (the gel inside your eye) can have tiny clumps of protein called floaters. When they drift near your line of sight, they can cast shadows on your retina and interact with incoming light, causing a shimmering perception.

In summary, the technical flicker of an LED is real but usually too fast to see directly. The radiating, pulsating halo you described is a beautiful example of a visual artifact created by the interplay of a bright light source with the natural, imperfect optics of the human eye.