Candlestick Chart

Description

The candlestick chart originated in 18th-century Japanese rice trading and has become the dominant chart type in financial markets. Each candlestick represents a single time period (day, hour, minute) and encodes four values: the opening price, the closing price, the highest price, and the lowest price. The thick “body” of the candlestick spans from open to close, while thin “wicks” (or “shadows”) extend to the high and low.

Color encodes direction: a filled or red body indicates that the close was lower than the open (a down period), while a hollow or green body indicates the close was higher (an up period). This color convention lets traders instantly scan a chart and perceive bullish or bearish momentum. Patterns of consecutive candlesticks form recognizable shapes (doji, hammer, engulfing, etc.) that technical analysts use to predict future price movements.

The candlestick chart is information-dense — four values per time period in a compact mark — yet highly readable once the convention is learned. It outperforms simple line charts for financial analysis because it reveals intra-period volatility (the wick length), directional movement (body color), and the relationship between open and close (body size), none of which a line connecting closing prices alone can convey.

When to Use

• Analyzing stock, commodity, or cryptocurrency price movements over time
• When all four OHLC values per period are available and relevant
• Technical analysis where candlestick patterns inform trading decisions
• Comparing volatility (wick length) alongside directional movement (body color)

When NOT to Use

• When only closing prices are available — use a line graph
• For non-financial data without open/high/low/close semantics — the encoding is misleading
• When the audience is unfamiliar with financial chart conventions — a simpler line chart communicates trend more clearly
• For very long time horizons (decades) at daily resolution — too many candlesticks; aggregate to weekly or monthly first

Anatomy

• Body: The thick rectangular portion spanning from open to close price. Color indicates direction (green/hollow = up, red/filled = down).
• Upper wick (shadow): A thin line extending from the top of the body to the period’s high price.
• Lower wick (shadow): A thin line extending from the bottom of the body to the period’s low price.
• Time axis: Horizontal axis with time periods (days, hours, etc.).
• Price axis: Vertical axis showing price values.
• Volume bars: Often shown in a secondary panel below the candlestick chart, with bar height encoding trading volume per period.

Variations

• OHLC bar chart: Replaces the filled body with a horizontal tick on the left (open) and right (close) of a vertical line, reducing visual weight.
• Heikin-Ashi: A smoothed variant that uses averaged OHLC values to reduce noise and make trends more visible.
• Hollow candlestick: Body is hollow when close > prior close and filled when close < prior close, adding a second comparison dimension.
• Renko chart: Ignores time and draws boxes of fixed price increments, filtering out noise.
• Kagi chart: Uses vertical lines that change direction only when price reverses by a threshold amount.

Code Reference

// Observable Plot - candlestick chart
Plot.plot({
  marks: [
    // Wicks (high-low)
    Plot.ruleX(data, {
      x: "date",
      y1: "low",
      y2: "high",
      stroke: "#888"
    }),
    // Bodies (open-close)
    Plot.barY(data, {
      x: "date",
      y1: "open",
      y2: "close",
      fill: d => d.close >= d.open ? "#22c55e" : "#ef4444",
      tip: true
    })
  ],
  x: { type: "band", label: "Date" },
  y: { label: "Price ($)" }
})