Trading sessions

Shade session hours with a background plot and box the developing session range with entities.

This example works with clock time instead of bar indices: it declares two UTC sessions, tints the background while New York is open, and draws a live box around the developing London range.

London session range boxes and New York background shading rendered from Binance Futures BTC/USD market data

script "Trading Sessions"

data chart = subscribe(data.ohlcv)

input (
  londonColor = input.color(color.blue, title: "London")
  nyColor     = input.color(color.orange, title: "New York")
)

state (
  london  = time.session("08:00", "16:00", name: "London")
  newYork = time.session("13:30", "20:00", name: "New York")
  boxes   = entities.boxPool(max: 8)
  inLondon:     bool   = false
  slot:         int    = 0
  sessionStart: time?  = null
  sessionHigh:  float  = 0.0
  sessionLow:   float  = 0.0
)

plot nyBg = plot.bg(title: "New York Hours")

on chart.update {
  let now = (chart.time ?? time.fromUnixSeconds(0))
  let barEnd = now + time.bars(1)

  // Tint the background while New York is open. Not calling plot leaves
  // the bar untinted.
  if newYork.contains(now) {
    nyBg.plot(color: color.withAlpha(nyColor, 22))
  }

  // Track the developing London range and draw it as a box.
  if london.contains(now) {
    if !inLondon {
      inLondon = true
      slot = slot >= 7 ? 0 : slot + 1
      sessionStart = (london.windowStart(now) ?? now)
      sessionHigh = (chart.high ?? 0.0)
      sessionLow = (chart.low ?? 0.0)
    } else {
      sessionHigh = math.max(sessionHigh, (chart.high ?? 0.0))
      sessionLow = math.min(sessionLow, (chart.low ?? 0.0))
    }

    boxes.get("london", slot).set(
      x1: (sessionStart ?? now),
      y1: sessionHigh,
      x2: barEnd,
      y2: sessionLow,
      color: color.withAlpha(londonColor, 28),
      borderColor: londonColor,
      borderWidth: 1.0,
      text: "London",
      textColor: color.white,
      textSize: 11.0,
    )
  } else {
    inLondon = false
  }
}

Sessions are time windows, not bar counts

time.session defines a repeating UTC window that works on any chart timeframe. contains answers whether the current bar falls inside it, and windowStart recovers the session's opening timestamp so the box can anchor to the true session start even if the first in-session bar arrives late.

One box per session instance

Each London session uses a numbered slot in the box pool. The pool holds eight boxes. When the ninth session starts, it reuses the oldest box.

Update the same box

On each bar during the session, set updates the same box with the latest high, low, and right edge. Supplying all its properties keeps the update simple.

Sessions are time windows, not bar counts

One box per session instance

Update the same box

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