Yes you should actually get familiar with the lighting ratios and yes, that means that you really should have paid attention during math class because it would make this portion of learning photography much easier on you! It’s actually not that bad but it does require that you put on the old thinking cap in order do decide on the correct exposure and to make sure that you remember that ratio so that you can duplicate the results the next time you need them
Lights, Ratios and Results
Your go to light is considered your main light. I know it’s a stretch for a concept but follow along. It’s not too difficult to remember but the ratios that we will be talking about here are in relationship to one another. In other words, if we were going to take a light using only our main light (we would not generally do this because the results are usually quite unflattering when doing this) we have an effective portrait photography light ratio of 1:0 or one to zero. In essence that is because we are using 1 main light at full power and no fill lighting of any type. In all of these equations we do not consider the ambient light into the figure. It can be done but it is far more complicated than it needs to be and the numbers really won’t matter that much on the ambient lighting in a NORMAL studio.
When using ratio, the common denominators are two numbers separated by a colon. So with light entirely off your lighting ratio would be 0:0 meaning that there is no main light which is the first number and no fill light which is the second number.
Using only one fill light will give you an effective portrait photography light ratio of 0:1 or zero to one. See how that works, pretty easy stuff right? You can understand it this way. But this is where the ease of use actually stops because we are going to change the power on those two lights and the ratios are going to get whacky on you.
If both the main light and the fill light are on and they are both at full power the equation for figuring out the ratio goes like this. The main light hitting the face has a value of one, the fill light hitting the side of the face has a value of one, one plus one equals two. So the lit side of the face is being hit by both lights and the fill side by only one so with both lights on full blast and set up this way we have an effective portrait photography light ratio of 2:1 or two to one.
At this point the sweat beads are starting as you are trying to fathom all of this. Don’t worry my friend, read on and you shall be enlightened (pun intended).
Now let’s assume that you cut the power to the fill light in half. That makes the main light on the face twice as bright so you have a value of two for the main light and a value of one for the fill light for a total of three. Thus we have an effective portrait photography light ratio of 3:1 or three to one. See, it’s getting easier to understand right?
Now if we take the fill light cad cut it back to one quarter power we are essentially making the main light seem as though it is four times as bright and we change our lighting in this example to an effective portrait photography light ratio of 5:1 or four to one. Meaning the main light is four times as bright as the fill lights. (The main light equals four, fill light equals one so 4+1 for the main light equals 5 and of course one for the fill light gives you the second number of 1. Now when it is put that way is this starting to make sense?
Remember as we go that the fill light is the second number it is a one in every instance. We are calculating how much brighter the main light seems when put in relation ship to that number one fill lighting.
If we continue down this line of thinking to the next cut on the fill light power, we cut it back to one eighth power output making our formula here eight times as bright on the main light plus adding in one for the fill light gives us an effective portrait photography light ratio of 9:1 which is nine to one with the main light seeming to be nine times as bright as your fill light.
It is not a hard concept to grasp when you actually step back and remember that we are talking about real life scenarios and not just number ratios. Now we’re going to look at the exact scenarios above in terms of f stop settings so that it will be even clearer for you. Using your light meter will make it much easier for you to duplicate your results time and again. You DO have a hand held light meter right? If not that needs to be on your wish list for birthday, Christmas or a “just because I need it” purchase.
F Stops instead of Numbers
In the words of a famous comedian, Well all righty then.” Let’s break it down into non numerical and rather photographic terms. That will give you two ways of looking at the idea and likely one of them should stick with you fairly easily.
Let’s consider out f stop mains setting at f 11. When you have your main light set for f 11 and your fill light off you get the 1:0 ration that we discussed so long ago in this article. One main light plus zero fill light against zero fill light gives 1:0 as your effective portrait photography light ratio. Aha, I saw a light bulb go off there. This is starting to make better sense now is it not?
A zero on the main light and using just the fill light at f 11 gives you 0:1 as your effective portrait photography light ratio. Yes, it really is going t be this easy now that you have looked at it from both methods of figuring it out.
An effective portrait photography light ratio of two to one involves both the main light and the fill light being of equal power at f 11 so it is one plus one for the main light and one for the fill light giving you two to one.
To achieve a three to one as your effective portrait photography light ratio, you will leave your main exposure setting at f 11 and your fill setting will drop back to f 8. This gives to two plus one for the main light and one for the fill and you get the three to one ratio that you were after. To put this in lingo that teenagers are using today OMG this is so cool.
Okay now class, if we are looking to make an exposure ratio of five to one, what do we need to do? That right, the main lighting having a value of f 11 and then dropping the fill rating to an f 5.6 and we are lost in the five to one lighting ratio that we were in search of. Amazingly simple once you understand both the mathematics and the dynamics of it now isn’t it?
Obviously if we drop the fill down to an f 4 that will increase the main setting sensitivity which remains at f 11 to eight times the amount of exposure so we add the eight for the main plus one for the fill against the main number and there we have our nine to one lighting ratio.
We could go one with example after example but if you don’t have the general idea by this point in time then you need to re-read the above information and if it still doesn’t sink in, then perhaps you should just use the time honored trial and error method. Nothing wrong with going by the book or using what you have discovered that works for you. The important thing is that you know that such things as lighting ratios exist and that you have started to think about lighting as a multi dimensional thing that can help or hurt your craft.
Photography as we know it would not exist without lighting and since we are all aware that the perfect lighting scenario does not exist in nature very often. We all need to find a way that will work for us to get as close to the perfect lighting as we can. It might involve you crunching some number and learning your exposure and f stops, it might involve your training your eyes to see the proper conditions and it just might be a combination of all of these thrown into a blender and mashed together to get the right results.