Comparing Output in Lumens

LUMENS:

The lumen is one of the most misunderstood and most misquoted values used in describing light output. A lumen is simply a measure of total visible light energy (luminous-flux) produced by a light source, and as such, does not consider the area over which it might be spread. It is also independent of distance. A 100 lumen bulb is a 100 lumen bulb at ten feet or ten miles.

You don’t measure lumens with a simple light meter. If you are using a lightmeter you are measuring illuminance, but not lumens. The typical light meter is measuring foot-candles, or their metric equivalent, lux, both of which are a measure of lumen-density, (i.e. lumens falling on a given area) but not lumens. Two bulbs with the same number of lumens can have very different illuminance readings. A bulb with a narrow beam focus will measure much higher lux than its wider-angle counterpart. This is because lux is a measurement of lumen density, but not total lumens.

To measure lumens, one needs either an integrating sphere, or a goniophotometer, something most folks don’t have lying around. Fortunately, here at Marinebeam, we have an on-site goniophotometer. It measures luminous intensity by angle, which is then mathematically cosine corrected, and integrated to calculate the bulb's total luminous-flux in lumens. Our competitors, on the other hand, will just take the theoretical maximum output from the LED supplier's spec sheet, and multiply it by the number of LEDs in their cluster. Unfortunately, it just doesn't work that way. The result from our most-famous competitor is a misstatement of lumen values of more than 70%! Another competitor has a lens on each of its products which focus the light into a narrow spot, so they measure lumen-density, and then make wild claims like 60 watt “equivalency”.

TOTAL EFFECTIVE LUMENS

Because halogens and fluorescents are omni-directional, and rely upon the fixture to direct the light, as little as 30% of the light illuminates the intended surface. LEDs on the other hand are directional, and up to 90% of the total output can be utilized.

Total Effective Lumens for halogens can also be influenced by fixture and reflector design, dirt and corrosion on the reflective surfaces, and luminous degredation of the bulb itself (tungsten coating the inside of the bulb). LEDs are mostly immune to these issues, as they don't rely on the fixture design or components to direct the light effectively. However, some factors like fixture lensing, dust, ageing, and material defects can influence the lumen effectivity of both incandescents and LEDs.

HALOGEN OUTPUT:

10W G4 Halogen bulbs are typically rated as high as 140 Lumens, and their Xenon cousins at about 100 Lumens. Given a typical reflective boat fixture with total Effective Lumens of 35%, we see that the 140 Lumen output is effectively about 49 Lumens at the work surface, while the 100 Lumen output works out to an effective 35 Lumens.

LED OUTPUT:

The Marinebeam G4 Warm White LEDs have a rated output of from 68 to 139 Lumens (depending on type). In the same fixture above, because we have directional light with LEDs, and are not not relying on the reflective surfaces, we have an Effective Lumen factor of 77%. The 68 Lumens therefore converts to 52 Lumens, while the 107 Lumens converts 92 Lumens.

So, we can see that in the typical marine fixture that the Marinebeam products match up well against their halogen counterparts, and with our high-output products one can expect an improvement over their existing 10W halogen or xenon bulbs.

LUMEN MAINTENANCE and LIFESPAN:

Both incandescent and LED's suffer from lumen depreciation. This is the phenomenon where, over time, the luminous output of the bulb is reduced.

Incandescent lumen output degrades relatively steeply as the filament begins to errode and tungsten and other materials off-gas and deposit themselves onto the glass globe. Incandescents typically end their useful lives in catastrophic failure after mere hundreds of hours of use.

LED's also suffer from lumen depreciation. Most LED's luminous output is recorded after some period of "warm up" were the LED's are allowed to stabilize, as the initial output from LED's can vary dramatically as they come up to temperature. It is not uncommon for LED output to depreciate 5-10% in the first 1,000 hours. Good thermal management practices can reduce this depreciation to the low end of this figure. Of course, at 1,000 hours the halogen is likely already dead, or has certainly depreciated more than 10%.

LED lifespans can actually be 100,000 hours or more, but they are typically rated to 70% of their initial lumen output. In otherwords, if the LED bulb has an L70 rating for 50,000 hours, that means that at 50,000 hours the output of the bulb has depreciated at least 30%. This threshold was chosen by the industry because the human eye has difficulty perceiving any drops of less than 30%. Be very wary of claims for high-output products of 50,000 hours or more, as they are likely not made considering the L70 standards.