Understanding Light Source Pulsation and Visual Perception

Great observation! Let's break down each aspect of light pulsation and perception:

1. LED and Artificial Light Flickering

Why LEDs flicker:

• Most LED bulbs are powered by AC (alternating current) and use drivers that convert AC to DC
• Cheap or poorly designed drivers can create flicker at 100-120 Hz (twice the AC frequency)
• PWM (Pulse Width Modulation) dimming rapidly switches LEDs on/off to control brightness

Visibility to humans:

• Most people don't consciously perceive flicker above 50-60 Hz
• However, peripheral vision can detect flicker up to 200 Hz
• Some individuals are more sensitive and experience headaches or eye strain
• You might notice it when moving your eyes quickly or seeing a light in peripheral vision

Other artificial lights:

• Incandescent bulbs: Minimal flicker (filament stays hot between AC cycles)
• Fluorescent lights: Noticeable flicker at 100-120 Hz, worse with magnetic ballasts
• Quality LEDs: Modern drivers with good capacitors produce minimal flicker

2. Does the Sun Pulsate?

Yes, but not in a way that affects our perception:

Solar oscillations:

• The Sun undergoes helioseismic oscillations with periods of ~5 minutes
• These are sound waves trapped inside the Sun, causing surface movements of a few km
• Brightness variations are incredibly tiny (~0.001% or less)

Solar activity cycles:

• The 11-year solar cycle causes ~0.1% brightness variation
• Completely imperceptible to human vision
• The Sun appears constant because these changes are far below our detection threshold

3. Are Any Light Sources Truly Constant?

Nearly constant sources:

• Incandescent bulbs (on DC power)
• Quality LED bulbs with proper drivers and capacitors
• Sunlight (for practical purposes)
• Laser pointers (battery-powered DC)

All sources have some variation:

• At quantum levels, photon emission is probabilistic and "noisy"
• Thermal sources fluctuate slightly with temperature variations
• However, these quantum and thermal fluctuations are far too small and fast for human perception
• For practical purposes, DC-powered incandescent lights are the closest to "perfectly constant"

4. Perception of Pulsation and Halos

This is where it gets interesting—most perceived pulsation is optical/neurological, not from the source:

Optical causes (your eyes):

• Diffraction: Light bending around iris edges creates radial patterns
• Lens imperfections: Astigmatism creates star-burst patterns around lights
• Pupil dynamics: Your pupil constantly adjusts, changing the amount of light entering
• Tear film: Uneven tear coating on your cornea refracts light differently
• Floaters: Cast shadows that move with eye movement

Neurological causes (your brain):

• Troxler fading: Staring at steady stimuli causes them to fade and reappear
• Microsaccades: Tiny involuntary eye movements make static images appear to shimmer
• Adaptation: Retinal cells adapt to brightness, creating perceived fluctuations
• Attention: When you focus on a light, increased neural activity can create perceived pulsation

Testing what you're seeing:

1. Record with a phone camera - if pulsation appears in video, it's real flicker
2. Look at reflection - if pulsation follows the reflection, it's the source
3. Cover one eye - if it changes significantly, it's likely optical
4. Look away then back - perception resets often indicate neurological processing

Most Likely Explanation for Your LED

Your observation is probably a combination of:

• Mild LED flicker (if it's a cheaper bulb without good driver circuitry)
• Optical diffraction creating a halo pattern around the bright source
• Your visual system's processing making you hyper-aware of the light when you focus on it

If the pulsation bothers you, try looking for LED bulbs labeled "flicker-free" or with specifications showing <5% flicker at all brightness levels.