Open Air Tutorials: What is a Lumen?

Anyone who has ever shopped for a digital projector will have encountered the word lumen with remarkable persistence. It appears in specifications, comparisons, and conversations, usually without explanation, as if everyone involved has already agreed on what it means. In simple terms, a lumen is a measure of how much light a projector emits—how forcefully it throws illumination into the world.

Once upon a time, this was known as candlepower, which sounds charmingly straightforward until you learn how it was defined. A single unit—called a candela—was based on the light emitted by one candle made from exactly 0.167 troy pounds of whale blubber, formulated to burn at a precise rate for exactly eight hours. This was considered perfectly reasonable, assuming you had ready access to whale blubber and a good scale. Fortunately, modern outdoor cinema no longer requires a background in marine harvesting.

Today, a candela is defined in a far more scientific way: the luminous intensity of monochromatic radiation emitted at a frequency of 540 terahertz, with a radiant intensity of 0.001464128 watts per steradian. This definition has the advantage of precision, even if it leaves most people nodding politely and hoping the subject changes. We will, in fact, leave the finer points of this measurement to the American National Standards Institute (ANSI), whose job it is to worry about such things.

For practical purposes, a lumen simply tells us how much light a projector produces. While it’s not entirely accurate to say lumens equal brightness, it is generally safe to assume that a projector with more lumens will produce a brighter image than one with fewer. What we’re really after is a projector capable of delivering images that are sharp and easy to see in normal ambient lighting—meaning your audience can actually see what’s happening without plunging the venue into near darkness.

To give an outdoor cinema event the visual punch it deserves, it’s important to select a projector that matches the venue and lighting conditions. The ideal projector produces clear, visible images even when some ambient light is present. There are several helpful resources available to guide you toward the right choice, and if questions arise, our support team is always happy to help. Measuring whale blubber is no longer required.