Engineering reference
Lighting specifications that survive contact with a site
Most lighting problems are not lighting problems. They are a maintained illuminance read as an initial value, a driver chosen on wattage instead of current, a UGR figure quoted from a catalogue that assumed a room nothing like yours. These notes cover the parts of a commercial LED specification where the datasheet and the installed result diverge.
Metrics & standards
What illuminance, glare, colour rendering and flicker figures actually mean, how they are measured, and the specific ways each one gets misread on a tender document.
Read the metrics notes
Selection & calculation
Drivers, dimming protocols, ingress ratings and emergency gear — the choices that decide whether a fitting works in year five, and the arithmetic behind them.
Read the selection notes
Retrofit & economics
Fluorescent and discharge replacement: what changes beyond the lamp, and how to build a payback case a finance department will sign off.
Read the retrofit notes
Acceptance & QC
Incoming inspection, colour consistency and ageing — checks that cost an afternoon and save a re-lamping campaign.
Read the acceptance notes
Calculators
Four browser-based tools: luminaire count by the lumen method, LED strip power and voltage drop, retrofit payback, and driver headroom. Each one shows its formula.
Open the calculators
Who writes this
We manufacture LED lighting and write the control software that drives it. These are the internal reference notes we use when specifying and inspecting our own product.
About this siteHow to read these notes
Two conventions run through every page here, and both exist because they are the places engineering writing usually goes wrong.
Standards are cited, not reproduced. Where a value comes from EN 12464-1, GB 50034, IEC 62717 or an IES document, we name the clause and tell you what it governs — we do not copy the tables. Those tables are the licensed product of the standards bodies, they are revised, and a number transcribed into a web page is a number nobody updates. Where a figure appears here it is either from a published manufacturer datasheet, with the source named, or it is an example calculation whose inputs are stated so you can redo it. Every document referenced anywhere on the site is indexed on the standards and sources page, with what it governs and where to buy the current edition.
Every number here has a stated origin. A figure on this site is one of three things, and the page always says which: a value from a named published standard or manufacturer datasheet, attributed to it; a worked example whose inputs are printed alongside the result so you can redo it with yours; or a measurement of our own, reported with the instrument, the test conditions and the sample size. We do not publish a plausible-looking number in place of one we can stand behind.
Where to start, by what you are trying to do
Writing or checking a specification. The three clauses that most often turn out to be unenforceable are illuminance, glare and colour. Start with maintained versus initial illuminance for why a lux figure with no maintenance factor specifies nothing, then uniformity and the compliant average for the requirement that a compliant average routinely hides, and UGR for why a catalogue glare figure belongs to a room that is not yours.
Comparing quotations. Efficacy is the number everyone compares and the one most often measured somewhere other than where it is quoted — where luminaire efficacy goes works the chain through. Then check the evidence rather than the datasheet: accredited, or just printed lists the nine fields that separate a usable test report from a document with a logo.
Planning a retrofit. The savings model is usually optimistic in predictable places. Retrofit payback is the arithmetic; lighting power density is the compliance ceiling that decides the product choice before efficacy does; and if the building has emergency fittings, the emergency circuit you inherited is the one section here that concerns life safety rather than money.
Accepting a delivery or a completed installation. Incoming inspection covers the checks worth an afternoon before anything is installed, and the handover pack lists the eleven documents whose absence costs a building for the next fifteen years.
What this site is not
It is not a design service and not a substitute for one. Lighting design for a real building involves fire strategy, emergency egress, controls commissioning and electrical safety, all of which need a qualified engineer with drawings in front of them and professional indemnity behind them. What you will find here is the layer underneath that: how the numbers work, so that you can read a proposal critically and ask the question that matters.