Quantity of Light

The amount of light there is – the Quantity – is a vital consideration. It’s very easy to overlook because not only do our eyes adjust very quickly to changes in quantity, but with automatic exposure modes, our cameras adjust too.

In manual exposure mode (which hopefully you’re using – go back to the Technical Course to learn more if you’re not!) you’ll have to adjust your exposure as the quantity of light changes in order to get a decent exposure. What you can’t escape though is the fact that the amount of light there is to play with will affect what combination of shutter speed, aperture and ISO you’re able to use. This, in turn, will determine some of your creative choices.

With “direction” we asked ourselves “Is the light coming from the direction I want it to?” With “Quality” we asked “Is the light as hard or soft as I want it?” With “Quantity” we need to ask ourselves, “Is there the right amount of light for the image I want to create?” Answering this will depend on what you want in your final image. Let’s say you want to use a slow shutter speed to blur the movement of water going over a waterfall. If the sun is shining, this may be challenging, as even with the lens stopped down to the smallest aperture, and the camera set to the lowest ISO, there may be so much light around that the slowest shutter speed you can get still freezes the water too much.

At the other end of the scale, if you need to freeze movement in something like a sports image, you’ll want a fast shutter speed. Imagine you’re indoors in a dingy sports hall, and you’ll realise that this may not be all that easy. You may find yourself pushing the ISO very high (and getting a lot of noise) and opening the aperture as far as it will go. Both of these compromises will affect how you shoot, and the answer might be to introduce more light in some way.

Dealing with variable quantities of light.

The essentials of Quantity are “Is there enough light to create the image we want to create?”

Having too much light can be dealt with by adding what’s called a Neutral Density filter, (or at a pinch a polariser). This functions just like a pair of sunglasses for your lens, cutting the amount of light that gets through. They are available in different strengths, each of which cuts out a different amount of light. Make sure you buy a decent quality filter though, since you’re putting it on the front of your lens, you don’t want to ruin the optical quality of your images with a cheap piece of glass. An ND filter will allow you to use a slower shutter speed, or a wider aperture, which you may require for whatever creative effect you’re after.

if you need more light, then you’re going to need to add some! This can get expensive and complicated as we start to get into different types of light such as flashguns, LEDs, Tungsten lights, all of which will be covered in more detail later in the course. Right now, all I want to talk about is the relative difference in quantity (or power, to give it another name) of different light types. This is important because you may need a certain amount of power to achieve a certain effect in your image, and you may also run into problems if you have light sources with hugely varying amounts of power.

In a situation like trying to reduce the shadows cast on someone’s face by the midday sun, the tiny, built-in flash in most cameras probably won’t have much effect, and you may need to either employ a larger, separate flashgun, or even a flash head of some sort. At the other end of the quantity scale, let’s say you’re shooting indoors in a room lit by small, household lamps, and you want to retain some of this mood in the picture. However, you also want to increase the quantity of light to give you a more usable exposure combination (such as a faster shutter speed, or smaller aperture). So, you go ahead and add in a great big tungsten light – something like the 1kw head seen in the video. You’ll now stand a better chance of getting the exposure you want, but you’ve totally killed the mood of the shot, as the relative power of the 1kw is so much compared to the 60w bulbs in the lamps, that they have been totally overpowered. A better solution in this situation might be to increase the light gradually, rather than in one big chunk.

Decent lights, of any sort, will allow you to adjust their power output across a wide range. The wider this range, the more useful the light is, as you can employ the same light to cover a variety of tasks. Something that has only full and half power is not as much use as something that goes all the way down to 1/128th power. In the same vein, the more precise this adjustment, the more precise you can be with your lighting, and this is particularly valuable when you’re combining the light from several sources. Being able to adjust light in fractions of a stop is very useful indeed!

Think back to the 4 characteristics of light, and you’ll realise that Distance (part of Direction) can be used as a primitive form of quantity control. To “increase the power” of a light, simply move it closer to your subject, and move it further away to reduce it.

Besides just adjusting the quantity of light, this same phenomenon must be borne in mind when we alter the quality of light. To make a hard light softer, we need to make it bigger in relation to the subject. There are many ways of doing this, but they’ll all result in some loss of quantity, as the light will have to travel further from the light source to the subject. If the light is bounced off something – such as a white wall, ceiling, or the silver interior of an umbrella or softbox – then that bouncing will increase the distance it needs to travel. If, instead, you choose to soften the light by placing some form of diffusion material in front of your light source, then the scattering effect that this has will also result in light having to travel further to reach your subject, thereby reducing the quantity.

This will have an obvious effect on your exposure, but it might also cause you to stop and think about your choice of light in the first place. Think back to our first hypothetical situation – trying to balance the light from the midday sun. If we use a flashgun, it may have enough power to do this, but as it’s such a small source (in relation to a person) it will cast a hard light. We may want a softer light than this, so we bounce or diffuse the flashgun. The light is now softer, but we’ve chopped off some of the quantity – possibly enough that the flashgun can no longer do it’s job, and we need something bigger like a flash head!

Add a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.