Day-night Test cricket is played with a pink ball rather than the traditional red one. The substitution exists because a red ball cannot be seen reliably under floodlights, and it has consequences well beyond visibility.
Red fails under artificial light
A red ball is visible in daylight against green turf, but under floodlights it darkens and merges with the surface and the sightscreen behind the bowler.
The problem is worst during twilight, when natural and artificial light mix and the colour temperature shifts rapidly across a single over.
White balls solve visibility but stain quickly against a dark sightscreen and cannot be used with traditional white clothing, which rules them out of Test cricket.
Pink is a compromise between two backgrounds
Pink retains contrast against both green grass and the dark background of a night sky, which is why it was selected after extended experimentation.
Achieving that required a heavier application of lacquer than a red ball carries, because the pigment sits differently and must be protected from scuffing.
That lacquer is the source of most of the on-field differences, since it changes how the ball behaves long before its colour becomes relevant.
The extra lacquer keeps the seam proud
A lacquered ball retains its shine longer and keeps the seam upright for more overs, which extends the period in which seam bowlers get movement.
Batters therefore face a genuinely new ball for longer, and the traditional plan of surviving an opening spell before scoring freely is harder to execute.
Conversely, the ball softens abruptly once the lacquer finally goes, so the transition from difficult to easy is sharper than with a red ball.
The twilight session distorts the match
Batting conditions are widely held to be hardest in the session when daylight fades and floodlights take over, and scoring rates typically fall then.
Because the schedule is fixed, one side may face two twilight sessions across a match while the other faces one, which is an asymmetry no toss can correct.
Captains take this into account when choosing at the toss, sometimes prioritising which session they will bat in over the state of the pitch.
The format was adopted for attendance
Test cricket played entirely on weekday afternoons competes poorly with work, and grounds in many countries were visibly empty for four of five days.
Moving play into the evening puts the final sessions within reach of a working audience, and attendance at day-night Tests has generally been stronger.
The trade is a match whose conditions vary more by time of day than by pitch, which purists dislike and administrators have accepted.
