Standards & compliance
How to read an LM-79 photometric report
An LM-79 report is the only independent proof of an LED fixture's lumens, efficacy, colour and distribution. Here is what each section means and the numbers to compare between suppliers.
By Hi-Looms Technologies engineering team · Updated 12 October 2026 · 2 min read
What LM-79 is
IES LM-79 is the test method for measuring the electrical and photometric performance of solid-state lighting products as complete fixtures, using an integrating sphere or a goniophotometer. It replaced the old habit of quoting LED chip lumens, which ignore driver, thermal and optical losses.
The sections that matter
Electrical
- Input power (W): the real consumption; compare with the rated wattage. A "100 W" fixture drawing 92 W is normal; one drawing 118 W will overheat.
- Power factor: above 0.9 for commercial and industrial fixtures.
- THD: total harmonic distortion below 20% keeps the fixture friendly to the supply.
Photometric
- Total luminous flux (lm): the headline number. Divide by input power for efficacy in lm/W.
- Luminous intensity distribution: the polar diagram. For street lights check the IES type (II or III) and the cut-off; for highbays check the beam angle (60°, 90° or 120°).
- Zonal lumen summary: how much light goes downward (0–90°) versus upward. Street lights should put at least 95% downward.
Colour
- CCT (K): correlated colour temperature; 5700–6500 K for outdoor, 4000 K for offices.
- CRI (Ra): 70 or above for roads, 80 or above for interiors and retail.
- Chromaticity (x, y) and Duv: fixtures in one batch should sit within the same ANSI bin so a row of lights looks the same colour.
Comparing two reports
- Make sure both tests were run at the same ambient temperature (25 °C) and after thermal stabilisation.
- Compare fixture lumens, not LED lumens; a report that lists chip data is not an LM-79 result.
- Check the sample is the model you are buying; look for the model number and photo in the report.
- Confirm the laboratory accreditation scope includes LM-79 or IS 16106.
Beyond LM-79
Lifetime claims need an LM-80 report for the LED package and a TM-21 projection for the operating temperature of your fixture. Surge immunity (IEC 61000-4-5), ingress protection (IEC 60529) and impact (IEC 62262) each have their own reports.
Hi-Looms supplies LM-79 reports with institutional quotations and lists the measured lumens, efficacy, CCT and CRI on every product page where testing is complete.
Frequently asked questions
What is the difference between LM-79 and LM-80?
LM-79 measures a complete fixture at a point in time: lumens, watts, efficacy and colour. LM-80 tests bare LED packages for thousands of hours to measure lumen depreciation, which TM-21 projects into an L70 life.
Should the report be from an NABL lab?
For Indian tenders, yes. NABL accreditation (ISO/IEC 17025) means the laboratory's measurements are traceable and accepted by government buyers.