Understand Light Units and Make Better Decisions When Buying Gear

Following the technological progress of recent years, LED panels are becoming ever more popular when it comes to lighting videos and, increasingly, photographs. Getting your head around the various units involved can be confusing so this video can be a useful means of learning what they mean and how they relate to one another.

Beyond a vague understanding that they give an idea of how much light something emits, watts, lux, lumens, and nits are a mystery to most people. If you’re about to invest in some LED panels, whether it’s something affordable like the Yongnuo YN600Air to help make your vlogs look a little more pro, or something a bit more serious like the Rotolight NEO 2, understanding what all of these figures mean can be critical.

In this short video, Gerald of Gerald Undone gives a very simple explanation of these measures of light and provides a means of understanding how you can compare an LED panel to a light bulb, which might be useful trying to figure out how much power and how many light sources you require. What’s more, if like me you’ve always wondered how many lux I’m achieving with one foot-candle, now’s your chance to find out.  As well as learning how lux differs from lumens, it’s useful to know how watts relates to them both, especially when you’re running your gear from batteries.

Be warned: Gerald does a great job of breaking this down but there’s a lot to take in in a very short amount of time.

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Alex Moan's picture


Bill Wells's picture

The person in the video is smart and understands everything he is saying. However, this was one of those, "Look how smart I want you to think I am" as opposed to "Here is how bright the bulb is".

I'm not saying the video is not interesting or needed. I'm just saying that most just want to know how bright is this light going to be when I turn it on.

I don't need to compare to a candle since I can't recall the last time time I used a candle for illumination. Just my opinion and I'm positive others who are more involved in light will love it.

He can't tell you how bright the light is; he is not shopping with you. He gave you the tool, now use it. You sound like the antagonist in the HomeAdvisor commercials.

“Really?!? Great!!! Can you compare the three top ones for me in an LCD setup, and check the reviews online, and verify the companies manufacturing them? Thanks!”

Bill Wells's picture

OMG. I did not mean to upset you. You need to take a deep breath and relax just a bit.

You see, just because someone is very knowledgeable does not mean they make a good teacher of the subject.

The question most photography have is, How does this LED compare to my 100w incandescent light? Didn't tell you that did it? No. In fact, it compares it to candles. I don't know about you but I haven't used a candle in years.

All I was saying is this topic could have been covered mush more effective with a more basic and realistic approach. That was all.

So calm down. I do appreciate you opinion, just not the anger and degrading remarks.

Do not read into things which are not there. I am not upset at all.

Taking deep breaths are actually not necessary for normal living, and I am quite relaxed. [tongue firmly in cheek]

Just because one did not grasp the subject matter, does not mean that one had a bad teacher. [tongue firmly in cheek]

«The question most photography have is, How does this LED compare to my 100w incandescent light?»
He addressed that. Re-watch the video. He mentioned why the Watt rating is meaningless. Re-watch the video. Some LED/CFL lights will compare itself with a “typical” incandescent bulb, but ① it is not specific, and ② if you have that, you do not need a guide.

«In fact, it compares it to candles.»
A very useful tool for a photographer, actually. 5 candles, one meter away provides about 5 lumens/m², which is about EV=1 @ ISO 100/21°. Everyone knows that! So now you can take better birthday pictures, (which is NOT where I last used a candle. That would have been a wedding).

What no one knows is, how many lumens does your particular 100W incandescent light produce. So no one can tell you how to convert that to a reasonable LED replacement.

«…more basic and realistic approach.»
I, for one, thought he did just that. Indeed, he was so basic, that he did not bog us down with the maths, and so realistic, he did not try to convert meaningless Wattage to lumens.

«…just not the anger….»
No anger. none at all.

«…degrading remarks.»
Sorry about that. Wasn't trying to be degrading. It just sounds as if you wanted him to do all the work, without all the knowledge. If you want to know how bright the light will be, that is almost always given in lumens, and it can be directly compared to other products which also give lumens, (which is most of the LED and CFL).


If we want to know that, there are way too many variables. Let's say that I want a one light portrait setup, where I want the light about 1.5m from the subject, and I want to use an aperture of f/8 (as that is my lenses “sweet-spot”), and a shutter speed of ¹/180 because that is my strobe sync speed and I want to minimise ambient light, and I want to use Sv= ISO 100/21°, so as to maximize my dynamic range.

Well, I have Tv, Av, Sv, and distance to light source. All I need to get now is Lv. With my manual strobe with a GN=60, I can work that out, unless…. But what I do have is an LED panel. Can I work that out given the lumens? No. because my strobe sends its light in one direction, but the LED panel does not. Oh, I can replace it with a non-360° LED bulb, but wait,…. What type of enclosure (if any) is it in? This begs the questions I would still have with my strobes; what modifiers am I using? what reflectors?

The best way of knowing is to set up the lights then use a light-meter, or do a test shot. Look at the Fstoppers article on the Godox AD400 vs the ProPhoto B10. One was rated at 400Ws, the other at 250Ws. Guess which one gave “more light”? So even this rating does not help one figure out “How much light?”

The question to which you want an answer is not one which one can address in a video, (and he made that clear).

Bill Wells's picture

Can I ask a question? What degree do you have, what school and date of graduation?

Regarding photography, or Physics/Mathematics?

Bill Wells's picture

No you seem pretty intelligent. Your website is pretty boastful (not a bad thing and I didn't intend it that way) but you never say you have a degree. I understand but, if you did have a degree you would have listed it or that I'm sure.

You hint to make the reader think you have a degree and extensive photography teaching at a university. But it appears it was a camera club of the University. None of that is bad.

I just think it is amazing how much people expand their knowledge without actually having a degree.

[EDIT] Sorry it took so long to respond. Life got busy. [EDIT]

No, I do not have a degree in photography. Never meant to suggest that I did. You are correct, that IF I had a degree in photography, I would have listed it.

As for expanding ones knowledge without a degree, that is done all the time. Look at Ansel Adams. Often credited with inventing the Zone system —no, he did not, and admits to as much; just expressed it in an easy to understand way— did not have any formal education in art. In fact, “Adams taught himself the piano, which would become his early passion. In 1916, following a trip to Yosemite National Park, he also began experimenting with photography. He learned darkroom techniques and read photography magazines, attended camera club meetings, and went to photography and art exhibits.” He then surrounded himself with other photographers.

It seems that he and I had quite similar education in photography. Mine started with reading the Time-Life series in photography at age thirteen, then getting tutored by a master photographer for a year at fourteen, then reading every photography book I could get my hands on at Munro College, the Manchester Parish Library, and the UWI Mona libraries. At the UWICC, Not only did I teach photography there for years, but, like any good art club, I continued to learn there from visiting photographers from different fields of photography, each with their own forte in the art.

My photography education, although not with a degree, and not from any single institution, is a solid one. It was also filled with many misconceptions which, over many years, I learned and corrected.

As for formal education, it was the end of summer after elementary school that I had finished reading (and understanding) my eldest sister's high school physics book, “Physics,” by A. F. Abbot. With four older siblings, I was always ahead of my own class. I started learning algebra (from my eldest sister), while still in elementary school. Simple equations and in-equations were easy. It took me a bit longer to grasp quadratics and polynomials, (not until after elementary school).

At age fourteen is when I taught myself programming; first Basic, then Pascal, then C, then Pascal with OOP and C++. I then went to UWI Mona to learn electrical engineering, (then Mechanical engineering), doing mathematics and physics courses, but then moved to Atlanta, where I decided to get a formal education in programming, having taught myself RDBMS, including QBE and SQL.

My maths teacher there pushed me back towards mathematics and physics, but, I still wanted to learn everything about programming and computers in general. I Then went back to UWI Mona, but the computer science faculty was full with a waiting list. I enrolled to do Physics, and continued learning Physics and math for two years before an opening came up in CS. Due to scheduling conflicts between final year courses in Maths and Physics with first-year courses in CS, I ended up doing first year courses in geology instead (to keep “full-time” status at UWI), and that is where my physics/mathematics studies ended.

Ended up becoming a business systems analyst, with a strong desire to break rocks open and stare at them and ponder. I used to have a vast photography portfolio of rocks, fossils, and sediments. ;-)

Bill Wells's picture

I was not saying you must have a degree to be intelligent or schooled. I was just wondering since you seemed to have a handle of the subject.

So the bottom line is, you do not have a degree of any type, in any discipline, issued by any university. There is nothing wrong with that. It was just a question - a compliment if you will.

What I don't understand is you were quick to say "I have no degree in photography". Making the reader think you might have a degree in something else. Then spend the next 7 paragraphs trying to use words that indicate you might have a degree in math or physics. Without saying you do not.

I was impressed with your knowledge of the subject.

I was intrigued with why you would dance around the question of having a degree.

Ah, no. I was responding to the original question, where I did not know which subject you were asking in which I had a degree . I did not know if you meant physics/mathematics, or if you meant photography. I was explaining my education only in those regards, where they came from, and how they (regarding physics/mathematics) stopped.

I did not think that CS nor Geology was relevant to the question, just peripheral information as to why no degree in Physics/engineering, yet so much knowledge.

Again, IF I had a degree in any field relevant to the discussion, I would have mentioned it. Even IF I had a degree in physics, engineering, or mathematics, I would not mention that on my photography website.

I think it is weird when I see a photography bio with something like, “I got my PhD. in Animal Husbandry from….” So although I mention that I taught photography in the UWICC, and that I sat on the advisory board of the PSCCA, I never mention what I was doing at UWI —nor Munro College— as it was not germane to my photography.

But, since this is the Internet, I tend to leave out most irrelevant info from discussions.

…And, yes, it may not have come across that way, but I did take it as a complement.

SUMMARY I never pursued (nor ever really contemplated pursuing) a degree in photography, and, although I did pursue a degree in physics/engineering, I sidelined that for computer science. If you want additional details, I would rather give it in a PM or something.

P.s., outside of geologists, thee is not a great deal of excitement over images of rocks, fossils, and sediments. :-D

Bill Wells's picture

I'll try one more time:

YOU DO NOT HAVE A DEGREE of any type, in any discipline, issued by any university? I understand that and we will just leave it at that.

“ PM me if you want more info,” is where I left it, but fine. We'll leave it here.

Bill Wells's picture

I wanted to put this link right at the top, just in case you don’t get to the bottom of the post.


Argument/position on why you may want to watermark your images. From here forward the term watermark will mean a logo or makers mark placed discreetly in lower part of image.

1 – Social media, regardless of if we personally like it or hate it is the venue for our marketing. We could expand that to include things like blogs and website galleries. We must all agree with this. Plus, the very importance of our images. Otherwise, there would be no need to have a website for your photography.

2 – One method of web search that has been increasing in the past few years, is image search. If that is true, then the importance of the knowing who made the image is critical. A watermark does that in just a glance.

3- Displaying your brand name on every image, some visitors may ask for permission to use your images. You may say, “Yes but some may not”. If that is your position, then you do not need to read this.

4 – If the image is shared by a visitor on Twitter, Facebook, Pinterest or Instagram. Your logo goes with it. From that share you could be hired or get a commission for permission to use.

5 – If someone removes your watermark, then the individual potentially faces stiffer legal penalties when your images are copyrighted.
When your watermark is removed by someone who has “reasonable ground to know, that [the removal] will induce, enable, facilitate or conceal an infringement” they have violated the Digital Millennium Copyright Act (DMCA) per 17 U.S.C. § 1202.
So, can an individual seal your work and claim free or fair use? Sure. It will just be harder for them to defend their position in a court of law.

Don't want to hijack this thread, so my short answer is, if it is going on the web, it will have a watermark.

Bill Wells's picture

I'm sorry, I did not mean to post this answer here. It was for another post. Sorry

Bill Wells's picture

The great thing about this video is, if you watch it twice. You will still have no idea how bright the light is. I'm sorry, this may be the worst video of all time.

Worst video of all time? If thats the worst video you've seen, then you must be living under a rock. Not only was it well produced but if you actually took the time to watch it, it made a lot of sense. Excellent video!

Bill Wells's picture

If this video intended to explain the intensity of light to a group of photographers, it missed the mark.

If the intent of the video was to show how much the maker knew about lighting, without regard to teaching the audience. Then it hit the mark.

Just because a person has a grasp on any complex subject, does not mean they make a good teacher. I sure you know that.

An effective communicator is one that can take a complex topic and explain it a manner that the audience understands and learns from.

It is precisely what it says it is; a photographer's guide to light units. It is a guide. Use it to guide you. It CANNOT TELL YOU what the intensity of your light is; it is not a measuring tool.

It is there to help you understand how YOU CAN COMPARE the intensity of a lumens rating of a bulb, with the lux rating of a panel, and make a decision. It also tells you why the watt and nits rating are not useful to photographers when comparing different technologies.

If you wanted him to tell you about your lighting, send him a sample. Better yet, send me all your lighting gear; I will do all the work, and tell you precisely how much light they produce. I just wont send them back, but at least you would know what you bought.

What precisely did you expect from the video? How can any video, «explain the intensity of light» with no context?

BTW, the video did not illustrate anything about how much (or little) he knew about lighting, just light units, as stated. He was dead on target.