Tag Archives: Fluorescent

Six things to know about light

'Let there be light' - Lighting is something every photographer has to work with

‘Let there be light’ – Lighting is something every photographer has to work with

Sometimes we cannot see bad light.

Our eyes compensate for the lighting in almost every indoor situation. We barely notice the colour of light. Unfortunately, our shots sometimes come out burdened with odd colours. Find out more…

Colour Casts

Almost every light source has its own colour. If the ambient light in a place is affected by the colour of the light our eyes ‘adjust’ that colour to white. When we take a picture with a camera it does not adjust, it faithfully reproduces it. Then, when we look at the picture, we see something called a ‘colour cast’. This is an odd overall colour in the picture. It’s caused by the colour cast affecting the colour tone of everything in the influence of the light. Normally, to get rid of the cast, we adjust our camera to this colour cast as white light – much as our eyes adjust. This is called ‘adjusting the white balance’. The light in the picture will look more like daylight again. We might not want to do that if the picture had the colour cast from, say a party, where the colours may be atmospheric. For many ordinary pictures that is not true and the artificial lights simply make the picture look odd.

Light Sources

Light sources are a range of things that produce light. Sources of light like bulbs or fires have very different origins and temperature, therefore the colour they produce is unique too. In photography our lights can strongly affect the outcome of our pictures. That is especially true if the light source has a colour cast. Photographer’s use of artificial light sources, like camera flash, studio lights and other photographic sources, needs care. Any old light will not do the job. We need to reliably create light without a colour cast. When manufacturers make light sources for photography they try to ensure that the light they create is ‘Daylight balanced’. Which means the light that is emitted by that source is a close colour-match to daylight or some other stated standard. Of course the colour of daylight varies – the colour of dawn and dusk is very different to a sunny mid-day or a rainy afternoon. Those colour differences are because of the affect that the atmosphere has on the light from the Sun. In fact, the Sun has a well known colour. So do other light sources.

Colour Temperature

The colour of a light source is a result of its ‘colour temperature’. The ‘colour temperature’ of a light is measured in temperature units called Kelvins, after the famous physicist Lord Kelvin. Kelvins are usually designated with a capital K – so we say 5,000K meaning five thousand Kelvins. The measure of Kelvins is important to photographers because the colour of the light needs to be defined.

By way of example it helps to think how an iron bar heats up. If we put iron in burning coals it gradually changes colour as it heats. First, it goes a very dull reddish colour. More heat and it goes bright red. As it heats more it gets orangey, then yellow. Next it turns slightly green then on to white – the hottest heat. The colours given off define the colour temperatures.

Our language confuses things. Sitting around the camp fire we are ‘warm’. As a result we think of our day to day ‘warm’ colours as reds. But actually they are cool colours on the Kelvin scale. Compared to the temperature of the Sun they are very cool! The Kelvin scale gives us the colour temperature indicators. The lower the Kelvin colour temperature, the more yellow to red the light. Higher colour temperatures is the bluer-to-white light range.

If we know the colour of light it helps us to describe it. For example:

  • Reds/yellows (2,700K to about 4,000K – Cool Kelvin scale colours)
  • Moonlight (4,100–4,150 K)
  • Sunlight overhead; electronic flash (5,500 K to 6,000 K)
  • Overcast daylight (6500 K)
  • Bluish/white (higher than 6,000K to 27,000K).

The colour temperature relates to the colour of a thermal light source. However, other light sources (eg. chemical or fluorescent) may have a colour on the colour temperature scale. They do not necessarily have an actual thermal temperature to match. So the colours are indicative and not actual temperatures. You might therefore burn yourself on a tungsten filament bulb – a thermal source. You might not burn yourself on a low-energy soft fluorescent bulb as the process for creating the light is not thermal. However, the colour the light produces can still be seen on the colour temperature scale. See a colour chart of colour temperature examples.

Incandescent bulbs

A light bulb with a filament creates light by the electricity heating the filament until it emits radiation. It’s a thermal source. Incandescent bulbs are really very inefficient. Only about 10% of their light is visible. Incandescent bulbs can create a strong colour cast. If you are shooting on auto-settings (and using *.jpg files) make sure you check any shot you take under such a bulb.

If you find you have an odd colour then you will need to adjust the white balance of the camera to get rid of the colour. Normally digital cameras have an easy menu setting for white balance. You may see it marked as a light bulb icon. Alternatively it may be called ‘Tungsten’. The latter is a metal often used in the filament of bulbs. The setting should compensate for your colour cast. Some bulbs may vary. So test by ‘chimping’ to get it right. Check your cameras manual to find out how to adjust the white balance setting. You should do it when you shoot, as you will not be able to adjust it later (unless you are shooting in a RAW file format).

Fluorescent lights

Strip lighting, or fluorescent tubes and modern low energy bulbs all produce a colour cast (unless daylight adjusted when manufactured). As with the light created by bulbs with filaments, you can adjust for it in your camera. There is generally a tube icon or a fluorescent setting in the white balance menu. Consider the light you are working with carefully. Not all fluorescent lights have the same colour and some settings on your camera may not be quite right for your setting. So be prepared to experiment.

The vocabulary of light

There are literally hundreds of words that describe light, its colours and various conditions and states. It helps to have a good vocabulary of light as you may find it easier to read about light and talk to others if you know the right terms. We have compiled a list of some of the most significant to photographers. We are also adding to it… So let us know if there are terms that you think should be in the list! You can find our ‘Light’ word list here.

By Damon Guy (author and Photokonnexion editor)

Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.

If you shoot with JPG, beware Auto-White Balance

"Test shot" - the ambient light in the room has created a yellow/red colour cast.

“Test shot” – the ambient light in the room has created a yellow/red colour cast. Removing this colour would be pretty impossible in *.jpg format.

It is ironic that people often shoot with the image format *.JPG because it seems ‘easier’. They can simply point and shoot with the camera on auto-settings. Well, precious photos are at risk. The *.jpg format dumps data when it is created in the camera.

Shooting in *.JPG mode is a problem. The data that is dumped leaves the file ‘baked’. Photographers use that term to describe a file where your options for change are limited. It’s a bit like a cake. Once the ingredients are baked, you cannot change the flavor of the cake. You might be able to make cosmetic changes. But you cannot change the fundamentals of the cake. So it is with *.jpg. If your colours or your white balance are off, you cannot change it.

Domestic florescent light bulbs (for example low energy bulbs) are some of the worst culprits for colour cast. They often create a bright yellow colour. The ‘Test Shot’ shown above is an example. Our eyes can normally compensate for the colour cast. The camera cannot. This ambient light shot has picked up a bright yellow cast – actually the background was brilliant white. It was white core board. The *.jpg format means that colour cast is there to stay.

Other colours may appear. Most common are yellows or steely blues. It depends on the bulbs that are present. So if you see these colours appear in your test shots, which is quite common, you need to compensate. If you read your camera manual you can look up White Balance. You will be able to find out how to compensate for these colour casts. In most cases digital cameras have white balance menu-settings for ‘tungsten’ and ‘fluorescent’. So it easy to select the appropriate setting. The next test shot will shot the colour as ‘true’ without the cast.

On the other hand, you can make it easy on yourself. Shoot in RAW instead. This is the type of file where the data in the file is retained. Then you can use an image editor – like PhotoShop or Elements – to change the colours when you are doing your post-processing. RAW files do no have the ‘baked in’ colour problem.

That brings me back to my original point. It is ironic that people think it’s easier to shoot in *.jpg until disaster strikes and everything goes yellow! Actually, since you cannot change anything, *.jpg is pretty hard to deal with at that point.

The motto of this story is… either get your white balance right when using *.jpg, or do the sensible thing and learn to shoot in RAW. The latter is easier and more flexible. And, you can save the day in ways that you cannot with *.jpg.

By Damon Guy (author and Photokonnexion editor)

Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.