When reading about LED flashlights and worklights, you might hear or read the following:
It has a lot of lumens.
Wow, it’s bright with 200 lumens.
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150 lumens for $5? That’s crazy-good value.
Oh the humanity, so many lumens!
I LUV the lumens!
OMG, so many lumens!
Lumens, lumens, lumens!!!!!!!
So what is a lumen?
The lumen (lm) is an international standardized measurement unit that tells you how much total light is emitted by an LED or other kind of light source. In more technical terms, it is a measure of luminous flux.
1 lumen = 1 candela * 1 steradian, where candela is a measure of light intensity and 1 steradian is 1/12.566th of a sphere.
(The steradian is defined as: a unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere that is equal to the radius squared. Source)
Sometimes you might see lumens out the front (OTF), which means a manufacturer has measured the lumens output out the front of their lighting product. This is in contrast to non-specified lumen ratings which might be based on emitter or bulb ratings.
The lumens rating of a flashlight will always be lower than the lumens rating of its bare emitter or light source, which is why some brands try to even the ground by explicitly saying their lumen ratings are based on OTF ratings. (This is analogous to how some cordless tools are marketed as 18V and others 20V Max*.)
What’s this lux stuff? Isn’t that smoked salmon?
You might also hear about lux (lx), which is a measure of luminous flux over a unit of area.
1 lx = 1 lm per square meter.
Lux tells you how light intensity is distributed, with measurements often taken at the center of the beam. You might sometimes hear lux related to a flashlight’s throw.
When comparing light sources with similar lumen ratings, a high lux value is often indicative of spot illumination, and a low lux value is often indicative of flood illumination.
Lux can be very misleading, as it can lead users to draw false conclusions without taking additional information into account.
(By the way, lox is smoked salmon. Never tried it.)
Foot-Candles
Sometimes you might see foot-candles (fc) used instead of lux. A foot-candle is the measure of luminous flux (lumens) divided by one square foot.
1 fc = 1 lm per square foot
1 fc = 10.764 lux
Candela
The candela (cd) is a measure of luminous intensity. Traditionally, one candela was the light intensity emitted by a common candle. It now has a more standardized and specific definition:
The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. Source: NIST
Some LED flashlights and products will include candela measurements for the middle of the flashlight beam. This, along with lumens, can also help give you a sense of a lighting product’s throw.
As with lux, candela ratings, generally offered as peak intensity measurements, can help in comparing the spotlight and floodlight nature of lighting products with similar lumen ratings.
According to the LED Resource, a candela/lumen ratio of over 100 suggests a strongly focused light source, a ratio of between 20-100 is common for tactical flashlights [and other higher-intensity spotlights], and a ratio of less than 10 is better for worklights [and other close-up lighting needs].
Questions?
I originally sought only to discuss lumens, but one thing led into another. If you have any questions, don’t hesitate to ask, and I will try my best to answer them. There are certain things I can’t do very well, such as describe steradian in easy to understand terms, and in those cases I will point to external references.
Fazal Majid
Another way to interpret lumens is they are dimensionally equivalent to watts, but lumens only measure the electromagnetic power that’s visible to human eyes. Thus 1 watt of pure green light (e.g. a laser) would be worth 683 lumens because the eye’s peak receptivity is in green, but 1W of infrared would be 0 lumens.
That’s why lumens/watt the measure of a light source’s effectiveness. For pure green light, the maximum possible would be 683, for white light the theoretical maximum would be in the 260 to 300 range, depending on color temperature. CREE and Philips have LEDs in the 200 lm/W range.
http://en.wikipedia.org/wiki/Luminous_efficacy
Stuart
While a lot of what you say is true, describing light output with watts can cause all kinds of confusion. As you suggested, not all power in = power out, and efficiencies have varied wildly over the years.
Michael Quinlan
Thanks. After your recent articles I was in Home Depot in the leftover holiday items section and saw some flashlights claiming “9 LEDs”. My immediate reaction was if you have a good LED, you only need one; boasting about the number of LEDs just tells me it’s a piece of junk.
Stuart
I have an older Inova with multiple LED and it’s actually quite good.
But you’re right. Most inexpensive multi-LED flashlights are junk. They’re good if you’re looking for a $2 flashlight, but don’t expect great performance from them.
Certain headlamps and other products have multiple LEDs because it creates a more effective way of increasing horizontal beam spread. Otherwise you have deal with larger and more complex products. So not all multi-LED products are bad.
Alvin Singh
I saw those as well and walked right by. I purchased the indestructible rayovac flashlight that was 50% off for $10. It is a great light!
Garrick
One of the best things about 110 volt LEDs is the electricity cost savings.
I spent a little time developing a cost/benefit chart of LED light bulbs for home/office/shop use. Typically, a “60 watt equivalent” LED bulb uses 1/10 cent per hour, as opposed to 6/10 cent per hour for a 60 watt incandescent bulb.
While a half cent an hour doesn’t sound like much, over a year (or say 1000 hours use, which is 3 hours per day), that’s a saving of $5. Since a good LED bulb costs about $15, that’s a 3 year pay back period. Some places have gov’t or utility sponsored subsidies. Home Depot in Bellingham WA has Cree Warm White “60 W” for $6 each, and some other lower quality LEDs for $2 and $3 each. The Cree warm white light output is indistinguishable from incandescents to my family and friends.
Since converting to LEDs in my home at a cost of around $260, my electricity bill has gone down about $20 a month. I’ve got most of my money back, and will continue to spend almost nothing on lighting for “22.8 years” (says so on the packaging). In fact… I do not save as much as I could because the cost is so low, I don’t worry about turning off lights anymore.
I did do some jerry-rigging to get all the lumens I wanted in some places, mostly via Y-sockets, which are those things that allow two bulbs in place of one.
Downsides:
You got to be willing to part with some cash.
100 watt equivalent bulbs are still not cheap. They run about $50 each.
They don’t give off much heat. Great in the summer, but I did leave my nice warm incandescent bulb in my beside lamp.
Upsides:
If they do last as long as they say, I may be in a retirement home before I ever have to change another light bulb.
You can increase light output in places where incandescents would be dangerously hot.
Less environmental damage, especially in areas where electricity is supplied by coal.
Kids (you know those little humans that always complain about being told to turn off the lights) become less costly.
Bill K
Thanks for the “lumen” technical discussion. The evolution in lighting is a technically fascinating!
This past fall I got interested in led lighting for landscape and motorcycle tail lights and I did a ton of research on leds, light design, and vendor sourcing. After this research, given that I didn’t want to experiment with a trial-n-error approach, I concluded that I could NOT engineer a led light that would produce the desired amoulnt of light in direction desired at a reasonable cost.
I did purchase a led flood light for landscape lighting for less than $20 and could not be happier. It is very bright and has circuitry to work on both ac & dc! I did find similar lighting for 6 to 7 time more ($120-140). To me this just points out that led lighting can and will be much cheaper in the long run, when real market competion takes hold.
I’d love to hear everyone’s related perspectives and opinions.
Bill K
From my research I also found one can find tons of aftermarket led tail light products that look good on the surface but don’t put out a lot of light, are not DOT approvable and are illegal in many states.
Here’s another market waiting for the technology and prices to drop.
For my motorcycle (actually a scooter) I wanted to add a bright third brake light. Again, since I didn’t want to experiment I found a commercial emergency vehicle light that is SERIOUSLY bright for a very reasonable, $50.
Dave L
A good side benefit of LEDs for brake and signal lights is that they come on noticeably faster than regular bulbs. This gives drivers behind you a little more notice when you stomp the brake to avoid the deer.
Dave L
As we see, lumens alone isn’t quite enough to judge a light-really helps to see what it actually does. WRT 110V LED lights, be aware they are more surge sensitive than incandescents. Whole-house surge protection is worth considering with them (and in general).
And Stuart, you really should try lox some day.:)
Ken K
The article was very informative.I am still confused.
Joshua Latham
Great information, a lot better than my own bright, brighter and brightest rating.
Richard D. Breen
In the candella section the frequency should read 540 x 10 to the 12th.
This works out to about 555 nanometers for a wavelength.
Stuart
Oops, you’re right. Superscript got lost in the pasting, so I added in a caret.
colt
is the max lumen or the saying up to 1200 lumens is that a faulse reading such as in stereo amplifiers have a max raitings but the true ratings are measured in rms
thank you
colt
Brian Stranahan
I have a customer looking to purchase one of 2 flashlights. One says it is 600 LUX and the other is 250 LUMENS. How can I tell which is “BRIGHTER”. This is an issue I constantly face. Any help you can give would be appreciated.
Thank you
Stuart
I’m not sure you can, at least not without testing them and measuring. And at that point, it would be simpler to do an A vs. B comparison.
caesar
Hey was wondering if im looking for a superbright flashlight doesnt matter if its throw or flood just want it to be intensley bright would i be looking for higher lumen or higher lux.
Thank you for your time
Stuart
If 2 flashlights are rated as outputting the same lumens, the one with the greater lux rating will appear brighter and more intense.
You’ll want higher lux, but also high lumens.
Rick
I want to know if a light boasts 5000 lux; is that equal to 5000 lumens I;e; 1 lux=1 lumen!! I saw an infomercial for a tactical flashlight that boasted 5000 lux; when I called the # to ask the question I could not reach a live person to speak to about it!
Stuart
No, lux and lumens are not the same.
Michael
What’s the better choice in a tactical flashlight? 5000 lux or 1000 lumens or is it that simple given the area of the light source space or origin is about the same?
Richard
From what I’ve read from other discussions, 5000 lux is equivalent to almost 500 lumens and 10,000 lux is equivalent to almost 1000 lumens.
Kirby
No. 1lumen will produce 1lux at 1meter sq. (3ft. Sq). So if u shine a flashlight with a rating of 500 lumens at a surface and the light is covering 1meter of that surface it would be 500lux (without taking into account any other variables). But if u cover 2meters it would be 250lux
Curt
There is a tv commercial that boasts that their flashlight is 5000 lux. They compare it to a 150 lux flashlight. I know that the 5000 lux is brighter but how much. I wonder why the tv commercials never use lumens when rating their flashlights.
Stuart
Probably because they’re hoping 5,000 lux will impress viewers, a large percentage of whom won’t be familiar with the terminology.
Stephen Stephen
Ok ,question if you have 32000 lumens,will 15800 lumens be the same in lighting
Geoffrey R.
I bought a Nebo Redline Blast and according to their website it says it’s their brightest flashlight, 1400 lumen. Then I was looking at their other flashlights and I noticed one that was about $20 more and I read the details and it says that it’s 3100 LUX. I’ve been pretty good at science and all even had electronics classes in tech school for the Air Force, but that was many moons ago. I’m just wondering which one of these 2 flashlights are the brightest, the 1400 lumen or 3100 lux? Great article but I’m still perplexed, not due to anything on your end, over the years I’ve had numerous concussions and several mental health problems. I will generally have to read the same sentence numerous times before I get that ah-ha moment of where I understand it. I do know that the flashlight I bought even with it’s 4x zoom is definitely bright, sometimes to bright for certain tasks especially if shining it on a white object, get way to much reflectivity. For those times I use my 300 lumen flashlight. Sorry for being long winded, just wondering if the 3100 lux is worth the extra money. How come they will put one flashlight in lumens and then a similar one in lux, is it to confuse people and get them to spend more for basically the same thing?
Stuart
Why is the Blast advertised in lumens, and the Select RC in lux? I honestly don’t know.
Robert Bragg
So, please answer the question. Which is brighter, 5000 lux or 1100 lumens?? Both products are available at about the same price.
Thanks
Stuart
There’s no way to answer that. You’ll have to ask the manufacturers for their full specs.
Einstein
Answer; 5000 lx equals to 500 lm. Hope this helps
Stuart
That simply isn’t true.
Let’s say you have a 100 lumen light source. In spot mode, it might throw all that light on a 0.093 square meters (around 1 square foot). So the lux might be described as 1075 lx. But let’s say it has a flood light design, and that 100 lumens is spread across 1 square meter. So then the lux might be described as 100 lx.
1 Lux = 1 lumen over 1 square meter.
When you have lumen values for 1 light, and lux for another, it doesn’t tell you anything.
Using only the information given, what’s heavier, 5 gallons of gravel, or 200 pounds of sand?
Waveform Lighting
I think the big takeaway we need to remember is that when discussing lux values, a distance and location needs to be specified. Is it 1000 lux at 1 ft? or 10 ft? These are two very different types of lights depending on the distance.
It isn’t very practical to do a lux to lumens conversion without knowing the beam angle of the lamp, either.
Chris
I am looking for a camping lantern or light and having the same problem… The “as seen on tv” model boasts 5000 lux. Another light says 700 lumens. How dpo u tell which will light up a campsite more brightly?
Stuart
You can’t.
John drove his car for 10 minutes, David drove his car for 10 miles. Who drove faster, John or David? In a similar matter, there’s not enough information to determine which is brighter.