Light
Flicker Is The Lighting Fault You Feel Before You See It
Many lights pulse faster than the eye can follow, and the result is felt as eye strain or headache rather than seen as flicker.
Some rooms are tiring to sit in for reasons nobody can name. A common cause is flicker in the lighting that is too fast to see but not too fast to affect you.
Mains power is not steady to begin with
Alternating current rises and falls many times a second, and passes through zero twice in each cycle. Any light driven directly from it pulses in step with that rhythm.
Older filament bulbs hid this well. The filament stayed hot between peaks, so its output smoothed out into something close to constant light.
An LED has almost no thermal inertia. It responds to the current it is given almost instantly, so whatever the electronics deliver is what the room receives.
The driver decides everything
Between the mains and the LED sits a driver, which converts the supply into something the diode can use. How well it smooths the output is the whole question.
A good driver holds the current steady and produces light with very little variation. A cheap one passes much of the ripple through and the lamp pulses noticeably.
Because the driver is hidden inside the fitting or the bulb base, this is invisible at the point of purchase. Two lamps that look identical can behave very differently.
Why you notice it without seeing it
Above roughly the rate at which vision resolves change, flicker stops registering as flicker. The visual system still processes the fluctuation, and for many people that shows up as fatigue.
Movement makes it visible again. A hand waved under a flickering lamp appears as a series of separated shapes rather than a blur, which is the simplest test available.
A phone camera pointed at the light often reveals banding on the screen for the same reason. Neither test is precise, but both catch the worst offenders.
Dimming can introduce it where there was none
Many dimmers reduce brightness by cutting part of each mains cycle away. With a driver that was not designed for it, the result is deeper pulsing at lower settings.
This is why a lamp can be comfortable at full output and unpleasant at half. The fault appears only in the condition where people most want to use it.
Matching the dimmer to the fitting, rather than assuming any dimmer works with any lamp, removes most of these problems before they start.
Where it matters most
Rooms used for long sittings deserve the most attention: desks, reading chairs, and anywhere a screen is in the same field of view as the lighting.
Workshops and kitchens have a separate reason to care. Rotating tools under a pulsing light can appear stationary, which is a genuine hazard rather than a comfort question.
Questions readers ask
Where should I hang a mirror to brighten a dark room?
On a wall adjacent to the window rather than opposite it, so it catches daylight at an angle and pushes it into the room instead of returning it to the glass.
Do mirrors really make a room look bigger?
They add apparent depth by reflecting space the eye reads as continuing. That only works if what they reflect is space rather than a blank wall.
