ANSI/PLATO FL1 is a measurement convention, and its usefulness is that it forces lumens, beam distance and runtime to be published together. The icons on the back of the box are not decoration; each one names a quantity and the conditions it was taken under.
The four figures the icons carry
The set normally shown is light output in lumens, beam distance in metres, runtime in hours and an impact and water rating. Some lamps add peak beam intensity in candela. The point of the convention is that a lamp quoting it has measured these quantities in a defined way, so two lamps quoting it can be compared field by field.
Where a lamp publishes a lumen figure and nothing else, there is no convention behind it at all. That is not necessarily dishonest, but it is not comparable, and it is the commonest situation on the cheaper end of the shelf.
What the runtime figure actually ends at
This is the part that surprises people. Under FL1, runtime is measured from switch-on to the moment output has fallen to one tenth of its initial value. It is not the moment the lamp goes out, and it is not the moment the lamp stops doing its job.
The consequence is that the number describes very different experiences depending on the lamp. An unregulated design dims continuously from the first minute and reaches the stated hours having spent most of them faint. A regulated design holds a level output and then falls away near the end. Both can publish the same runtime honestly. Only one of them gives you that light for the duration.
Makers who regulate output say so, usually in the specification table rather than on the front of the box. If nothing says it, read the runtime as a ceiling rather than as a description.
The lumen figure under FL1 is taken at a defined point after switch-on, and it describes the highest setting. On a modern lamp that setting is held only briefly before thermal management steps it down, because the LED and its housing cannot shed the heat indefinitely.
What matters for use is the output the maker publishes for the sustained level and the runtime beside it. Most makers publish a runtime for a middle setting as well as the maximum, and that middle row is the one that describes an evening.
Beam distance and what it does not tell you
Beam distance in metres is derived from beam intensity: it is the distance at which the light has fallen to a defined low level, taken as roughly the illumination of a full moon. It describes throw, not usefulness. A tight spot beam reaches a long way and lights a narrow circle; a flood at the same lumen figure reaches less far and lights the ground you are walking on.
Lamps with more than one beam pattern publish a distance for each. Reading only the largest figure will point you at the narrowest beam in the range.
The ingress and impact ratings
The water and dust figure is an IP rating, and it is worth reading in full rather than as a word. The impact figure is a stated drop height in metres onto a defined surface, and it tells you that the lamp survived that drop rather than that it is unbreakable.
Neither figure covers the battery compartment being opened in rain, and neither covers the cell itself in cold. Those are the two ways a rated lamp still lets you down.
Reading a specification table quickly
Take the middle output row, not the top one. Note the runtime on that row, whether the word regulated appears anywhere, the beam distance for the pattern you will use, and the IP rating. Five fields, all published, and all comparable between lamps that name the convention. A lamp that names no convention cannot enter that comparison, whatever its headline says.
What people ask before buying
Does FL1 mean the figures were checked by someone independent?
No. It is a common measurement convention rather than a certification scheme, and the figures are the maker's own. Its value is that two lamps quoting it have measured the same quantities the same way, which is more than can be said for a bare lumen number.
Why is the runtime so long when the lamp is dim after an hour?
Because the runtime figure ends at a tenth of the initial output, not at the point the lamp stops being useful. An unregulated lamp spends most of its stated hours well below its opening brightness. Lamps that hold a level output usually say they are regulated.
Last reviewed 6 September 2026