Photometric charts are essential tools for understanding the lighting performance of fixtures. They provide crucial data to evaluate how light interacts with a space, helping designers and engineers make informed decisions.
Here’s a step-by-step guide to reading a photometric chart.
What Is a Photometric Chart?
A photometric chart is a graphical representation of a light fixture’s performance. It typically includes details about:
- Light distribution – how light is emitted.
- Illuminance levels – how bright the light is at various distances.
- Beam angles – the spread of light.
Components of a Photometric Chart
1. Iso-Illuminance Curves
These curves depict how light intensity spreads across a surface. The chart is divided into zones, with each zone representing a specific illuminance level (measured in lux or foot-candles).
- Closer curves: Higher intensity at a smaller area.
- Wider curves: Light spreads out, lowering intensity.
2. Polar Diagram
The polar diagram shows light distribution in a two-dimensional plane, typically in:
- Vertical Plane: Light distribution along the height axis.
- Horizontal Plane: Spread across a room or surface.
3. Candela Distribution
Candela distribution charts show how the intensity of light varies with direction. The central peak shows the strongest intensity directly beneath the fixture.
Steps to Read a Photometric Chart
Step 1: Identify the Fixture Type
Before diving into the chart, understand the type of light source (e.g., LED, halogen) and its intended application.
Step 2: Understand the Scale
Each axis on the chart (vertical and horizontal) represents distance or intensity. Check the scale to interpret the data accurately.
Step 3: Examine Beam Spread
Use the polar diagram to understand the beam angle. This information tells you how wide the light spreads from the fixture.
- Narrow Beam (Spotlight): Concentrated light, suitable for highlighting objects.
- Wide Beam (Floodlight): Dispersed light, ideal for general illumination.
Step 4: Analyze Illuminance Levels
Iso-illuminance curves provide data about the light intensity at different points. Cross-reference these levels with your project’s lighting requirements.
Step 5: Check Energy Efficiency
Compare the lumens output (light generated) with wattage to assess efficiency. This is often listed alongside the photometric chart.