Reading Lumens and Run Time on a Spec Sheet

Why a peak lumen figure tells you almost nothing on its own, and what to ask for instead.

Two lanterns both advertise 400 lumens. One runs for five hours at that level, the other for forty minutes. The lumen number was true in both cases and told you nothing.

Always Ask for Lumens With Hours Attached

A useful specification pairs each brightness step with a run time. The Lamp2Torch is a good example of how it should read:

Setting	Output	Run time
Normal	25 lumens	100 hours
Night light	100 lumens	22 hours
High	200 lumens	11 hours
Super	400 lumens	5 hours

Notice the shape. Doubling brightness roughly halves the run time, which is what a well-behaved product should do. If a spec sheet claims high brightness with barely any run time penalty, something is being measured optimistically.

How Much Light Is Actually Enough

15 to 45 lumens. Reading and studying at a desk. This is the pico range: the SunBase at 40 lumens, the SunAwada at 40 to 45, the reading lamp without stand at 15.
100 to 270 lumens. Lighting a room to move around, cook and eat. The SunGold President reaches 270 lumens, the SunAce-Li 200.
375 to 400 lumens. A whole room brightly, or a shop stall trading after dark. The SEHEN lamps are 375 lumens each and the Lamp2Torch peaks at 400.

Efficacy Tells You About the LED

Lumens per watt is the efficiency of the light source. The SEHEN lamps are specified at a minimum of 125 lm/w, which means more light for the same battery drain. Where a spec sheet gives efficacy, it is usually a sign someone measured rather than estimated.

Charging Time Is Half the Story

A lantern that runs 10 hours but needs 10 hours of full sun is only useful in a place that gets 10 hours of full sun. Typical charging times across the range are 8 to 10 hours, and the street lights are 5 to 8 hours. Compare that against the sun your market actually gets in its worst month, not its best.