A photometric file isn't a brochure. It's a measured map of intensity in candela at every angle around the fixture. The goniophotometer measures it; DIALux models with it. Both are how a fixture becomes a design, not a guess.
Four ideas to carry into the next specification conversation you have.
A two-axis arm rotates a calibrated detector around the fixture. Every 1–5° it logs candela. Output: 1,000–10,000 data points.
B-gamma for car headlights, sports field projectors. C-gamma for almost everything else (downlights, streetlights, panels). Confusing the two breaks your DIALux model.
IES = North American (IESNA). LDT = European (EULUMDAT). DIALux reads both. Premium fixtures ship both files.
Free software, German engineering. The industry standard. Every NLC fixture ships with a DIALux-ready file.
Fields per IES LM-63-2019; commercial DIALux/AGi32 software uses all of them.
| Field | What it carries | Why it matters |
|---|---|---|
| TILT | Mounting tilt (NONE / line / file) | Streetlight aim correction |
| Number of lamps | Count of light sources | Bulb/source modelling |
| Lumens per lamp | Source lumen output | Validates total flux |
| Candela multiplier | Scaling factor (usually 1.0) | Re-scale for different flux |
| Horizontal angles | Number of phi (C) angles | Resolution around fixture |
| Vertical angles | Number of theta (γ) angles | Resolution above/below |
| Photometric type | 1 (Type C) / 2 (Type B) / 3 (Type A) | Coordinate system |
| Candela grid | Intensity at every (C, γ) | The actual photometry |
| Ballast factor | Driver dimming reference | Updates real-world output |
| Input watts | Total fixture power | Efficacy calculation |
Five things to know about photometric files and how to read them.
For an accurate measurement the detector must be in the fixture's far field, typically 5–30 m depending on aperture. Major LED makers have purpose-built labs (Independent Testing Labs in Massachusetts, ITL in Australia, LISUN in China). Look for an LM-79 report from an ISO-accredited lab.
LM-79 measures total luminous flux, efficacy, CCT, CRI, chromaticity. LM-80 measures lumen maintenance over time (3,000–10,000 hours of aging data, used to project L70 life). A spec citing only LM-79 is incomplete.
Old fluorescent files used relative photometry, lumens from a separate lamp test, candela distribution from the fixture. LEDs use absolute photometry, both measured together, since the LED and fixture are inseparable. LM-79 mandates absolute.
DIALux models direct light + 1st-bounce inter-reflection well. It struggles with specular surfaces (polished marble, mirrors) and complex daylight. For atriums, malls, museums, switch to AGi32 or Relux for proper ray-tracing.
A DIALux report predicts ±10% lux. A real commissioning measurement should match within ±15% (accounting for paint variance, MF, and meter accuracy). Discrepancy > 25% means re-check the IES file, the room geometry, or the fixture install, something is wrong.
Every fixture in our catalogue has full LM-79 and LM-80 reports from accredited labs, plus DIALux-ready IES and LDT files.
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