– To see, or to be seen –
We have been asked on a number of instances what foot candles our lights will give at a certain distance, and then yet others will want to know it in terms of lux. So we thought it might be beneficial to clarify what some of these terms mean and further try to differentiate how an LED will differ from a traditional incandescent light in terms of illumination.
The technical definition is the “amount of light cast on a surface one candela source, one foot away” or maybe better said as ‘one lumen, one foot away’. What’s important is it is a standard unit of measure to reflect lighting levels at the lights point of direct contact. Here in the U.S. it is the most commonly referred to illumination measurement and it is a relative gauge of light that is used across a number of applications, such as parking lots, garage bays, shopping malls, and even in mining.
Where a foot candle is an imperial unit of illumination measurement LUX is a metric unit of illumination measurement and is calculated as 10.764 lux to every foot candle. One lux is equivalent to one lumen spread over one meter. In other words one lux will provide less illumination than one foot candle; so lux offers a more exact measure of illumination than foot candles, all things being equal. For reference, and depending on distances an office corridor will usually be lit to around 100 lux; a typical warehouse will be lit somewhere between 100-200 lux (10-20) foot candles.
Lumen: Since we mentioned lumens in the units of illumination measurements, it’s worthwhile discussing its relationship to Lux/ Foot candles.
Lumen is the total amount of light produced by a light source, and unfortunately the genesis for a lot of confusion when evaluating LED fixtures to that of traditional Metal Halide types. For example, a 500W Metal Halide Lamp (on average) will produce over 40,000 lumen, but greater lumen generated does not always equate proportionately to greater lux or foot candles within a defined area. Consider: our PX80 produces 28,000 lumen and is commonly used to replace 1000W Metal Halide fixtures on electric Shovels and Drills, and yet the 500W Metal Halide lamp produces 40,000 lumen(?) Incidentally, lumens are not to be confused for Watts, as Watts is a measure of power consumed not light produced.
Apples and Oranges: We often consider the lumen evaluation between traditional fixtures and LED fixtures as an apples to oranges comparison. This difference in measures is a big issue of confusion.
The spherical design and bulb/filament of a traditional fixture light is produced in a 360 degree radius and with reflectors is directed towards the intended area, where much of the light is increasingly dissipated further from the fixture the light travels. Whereas with LED fixtures, the design is hemispherical and light is directed 100% at its intended target area often producing more Lux at the same distance than that of a traditional fixture.
To Be Seen or To See: any LED light will afford you the capability of being seen, but what’s more important to our customers is what they can see with their lights. A light bar, for example offers significant illumination and the ability to be seen, but often suffers significantly in its capacity to provide adequate levels of illumination to properly see. Be sure to evaluate a fixtures capability by what you can see vs. another fixture. Using a tinted piece of glass will also allow you to look directly at the fixture as well, to determine any differences in illumination performance.