Accurate task lighting is critical for productivity, visual comfort, and safety in offices, labs, and industrial settings. The point-by-point method offers a reliable way to calculate light levels at specific locations, ensuring compliance with standards like EN 12464-1 or IESNA.

The principle is straightforward: for each luminaire, apply the inverse-square law and add contributions from all fixtures. Begin by mapping the workplane (typically 0.85 m above floor). For a given point P(x,y), calculate the horizontal illuminance Eh from one luminaire using Eh = (I(θ) × cos³(θ)) / d², where I(θ) is the intensity in candelas from the luminaire’s photometric data at angle θ, and d is the distance between luminaire and point. Sum Eh values from every fixture that influences that point.

Consider a small office with four recessed LED panels (each 3000 lm, spacing 3 m × 2 m, mounted at 2.8 m). For the center point: distance to each panel ≈ 1.8 m, θ ≈ 32°, I(θ) ≈ 1800 cd. Eh per panel = (1800 × cos³32°) / 1.8² = (1800 × 0.71) / 3.24 ≈ 394 lux. Summing four panels gives ~1576 lux—well above typical 500 lux requirement. However, at a corner point, contributions drop quickly, revealing zones below 300 lux. The designer then adjusts luminaire placement or adds supplementary fixtures to achieve both target level and uniformity (U0 > 0.6).

For complex spaces with shelving or partitions, divide the area into a grid (e.g., 0.5 m intervals). Plot a contour map or use software to visualize hot spots and shadows. The point-by-point method also supports calculations for vertical surfaces (e.g., reading a file label) by using a similar formula with vertical angle components.

Remember: factors like lamp lumen depreciation (LLD), dirt depreciation (LDD), and room surface reflections require correction. Apply LLF (Light Loss Factor) values—typically 0.70 to 0.85—to ensure real-world levels match design targets.

Mastering point-by-point calculation empowers lighting designers to deliver precise, energy-efficient task illumination, reduce rework, and enhance end-user satisfaction. Start with simple layouts and refine with practice.