A 5000-lumen narrow spot and a 5000-lumen flood are wildly different fixtures. The lumens are total output; what matters is how those lumens are distributed in space. That distribution is described in candelas, cd in each direction, and packaged in IES (USA) or LDT/EULUMDAT (Europe) photometric files.
Four ideas to carry into the next specification conversation you have.
Intensity = lm / sr. A 1000 lm fixture with 10° beam = ~36,500 cd at peak. Same flux, wide flood = ~80 cd peak.
Beam angle = where intensity drops to 50% of peak. Narrow spot 10°, medium 25°, flood 60°+, wide flood 90°+.
Field angle = where intensity drops to 10%. Useful for predicting spill light beyond the main beam.
DIALux/Relux read IES/LDT to compute lux on every surface. The file is the geometric distribution of light leaving the fixture.
Beam-angle categories and typical applications.
| Class | Beam angle | Use |
|---|---|---|
| Very narrow | < 10° | Object accent, jewellery |
| Narrow | 10-20° | Art, retail hero |
| Medium | 20-40° | Retail general, gallery |
| Wide | 40-60° | Office, downlight |
| Very wide | 60-90° | Flood, façade |
| Asymmetric | Wallwash | Wall illumination, signage |
Five things to check in any photometric file before specifying.
Where does the brightest cd point? At nadir (straight down) for downlights. At angle for tracks. The peak tells you where the fixture 'aims.'
Some IES files have lumen flag at 0 or wrong scale. Always cross-check claimed lumens vs the IES file's computed total.
An IES file should reference the lab and test date. NLC files include LM-79 lab name, accreditation, and goniophotometer model used.
Older IES files don't carry SPD. Newer LM-79 reports include SPD as separate data. NLC delivers both.
Dark-sky compliant fixtures have a hard cutoff at 90° (no light above horizontal). Check the cd vs vertical-angle curve.
Download IES + LDT files for every NLC luminaire. LM-79 lab traceability, SPD attached, dark-sky compliance flagged. Plugs into DIALux / Relux without conversion.
Practical lighting know-how from NLC Academy. No spam, unsubscribe anytime.
By subscribing you agree to receive NLC emails.