Almost daily, we get questions about how many Lumens a scene/work light emits. While we understand why people are asking this, this is really the wrong way to judge a light’s output.
There are really 3 main ways to judge the brightness of a light;
- Lumens – this is the total light that a lighting fixture emits in all directions.
- Candela – this is the light that a fixture emits in a certain direction.
- Lux – this is the measurement of how much light hits a surface to illuminate it.
Let’s start with Lumens because that is what most people (and companies) use when comparing various scene lights.
As you can see (hopefully) from the diagram above, Lumens show the total amount of light put out from a light source. With LEDs, this gets a bit tricky because most manufacturers use what they call “Raw Lumens“.
I would suggest that this is the most misunderstood term in the scene/work lighting world. What this means is that they haven’t actually measured the light coming out of a fixture. Rather, they are going by the LED manufacturer’s specifications for the LEDs themselves. If Cree (or whatever LED manufacturer) says that each LED emits 100 lumens, and the light manufacturer puts 10 of these LEDs in a fixture, then the manufacturer somewhat erroneously claims a 1000 Lumen output.
The difficulty with this measurement is that there are many factors to the brightness of an LED. For example, even a clear lens can suck up over 10% of the light output. If there are any optics to ‘bend’ the light in any direction, those can consume over 30% of the light. As the LEDs warm up, they can grow dimmer if the heat is not properly removed. So, in an extreme case, a 5000 lumen light can only really put out 2500 lumens. Why do manufacturers do this? First of all, because it’s easy – the manufacturer of the LED gives them the specifications for each LED so the manufacturer of the light simply adds them up and declares a “raw Lumens” number. Second, most manufacturers use this “raw” method so to have an actual Lumen measurement would mean your light is “dimmer” (on paper) than the competitors’. So, everyone tends to use the “raw Lumens” method.
We have had customers buy a 5000 lumen light that is twice the price, thicker, heavier, with a worse warranty, than a 4700 lumen light, just because of that extra 300 lumens. Of course, whether they can tell the difference in intensity of the light on the ground is unknown.
Very few, if any, manufacturers use Candelas for scene/work lights. They are quite common with warning (flashing) lights as that’s what SAE uses to measure a light. In the case of scene lights, however, pretty much no-one uses Candelas. So, let’s skip right over to Lux…
Lux is the measurement of light on a surface. Lux is the metric version of an older term you’ve probably heard of; foot-candles. Lux is a much more accurate and desirable measurement than Lumens.
You’ve probably seen a photographer with a handheld light meter, putting it beside a model’s face and triggering the flash to see how much light is being splashed on the subject? That photographer is measuring in Lux (they use a different scale, but essentially they are measuring Lux). You’ll note the photographer is not measuring right at the light itself, but rather where the light is hitting.
A Lux is 1 lumen covering 1 square meter. How does that equate to real life? Roughly speaking, 1 lux is about the equivalent of twilight. Your office is probably around 400-500 lux. A dark overcast day would be about 100 lux. Full daylight is 10,000-25,000 lux, and direct sunlight can get up to 100,000 lux.
Lux vs. Lumens
Clearly, the end goal of scene/work lighting is to light up a working surface. Really, do we care how bright the light on the side of the truck is, as long as it emits the proper amount of working light on the ground?
Here’s an example; Manufacturer “A” has a scene light that uses 10 x 100 Lumen LEDs (according to the LED manufacturer). They put these in a light fixture but put them behind a thick, aggressive lens to “bend” the light down to the ground. Also, they don’t have a great heatsink on the back so the lights dim 25% after they warm up. The manufacturer claims 1000 lumens but at 10′ from the vehicle, the measured light on the ground is 100 lux.
Manufacturer “B” uses 8 of the same LEDs in their light. However, they use a much more efficient optic and power/heat-sink system so that the lights emit 95% of their rated Lumens. When measured at 10′ from the truck, Manufacturer “B’s” light emits 150 lux., yet the manufacturer can only claim 800 Lumens.
Which light is brighter? The one that emits more Lux at the same distance from the light. The Lumens, in this (and many cases) are irrelevant. Generally speaking, a 5000 lumen light will be brighter than, say, a 1000 lumen light. However, a 5000 lumen light may or may not be brighter than a 4700 lumen light, for example. The 4700 lumen light may be more efficient and have better optics so that it’s actually brighter, or at least the same as the 5000 lumen light.
Watts deserves a mention here as well. Can you judge the brightness of a light based on watts? Not at all, especially if you’re talking about LEDs. Watts is simply a matter of how much power a device draws. You could have an efficiently-designed light that draws 60 watts at puts out 400 lux @ 10 meters, or you could have a poorly engineered light that draws 90 watts yet puts out only 200 lux. It’s like trying to estimate the horsepower of a car strictly from its gas consumption numbers.
Another trick some manufacturers will do is to create a ‘hot spot’ in their light pattern to allow them to increase their rated numbers. They measure their light intensity (candelas or Lux) at this bright spot and say “peak intensity = xxxxx”. The keyword there is “peak”.
It tells you how bright the brightest part of the beam is, but doesn’t tell you how bright the rest of the light is. Ideally, you want a nice even light pattern with no ‘hot’ spots. Most manufacturers have “polar plots” or other light-pattern drawings that show these kinds of hotspots.
The polar plot here shows a popular LED “flood” light. You’ll note the extreme hotspot in the middle of the light pattern, that is only roughly 30 degrees either side of center, and only about 10 degrees high. It’s certainly not an ideal flood light pattern, but hey – it’s rated at 16,000 lumens and has a draw of 166 watts, so it must be bright, right? Your impression, when you stand in front of it at night, is that it’s a really bright light – and it is…right in the middle.
Here is a great video done by Command Light that helps describe this a bit more:
We hope this helps you understand why Lumens are really not that important and why Lux is a much better comparison between lights. Contact us if you need more details.