Exercise: Tungsten and fluorescent lighting

Tungsten and fluorescent lighting prove to be particularly challenging, especially fluorescent which has a narrow colour spectrum.  Tungsten lighting, in a domestic and commercial environment, is now less common, and has not been available to the consumer for several years, at least in the UK.

I tried to make sense of what colour temperature settings should one be using with this type of lighting, including the Compact Fluorescent Lamp (CFL), as I have always experienced difficulty, particularly with the strong colour casts on photographs taken under fluorescent lights.  I was also interested, going forward, what will be happening with regard to LED lighting, as, looking at the manufacturers' websites, such as Philips and Osram, LED lighting appears to be the product which ultimately will replace Fluorescent or CFL as well as incandescent light sources such as Halogen bulbs.

Wikipedia was my first stop and, though not helpful for incandescent lighting, the entry for fluorescent lighting was much more revealing.  This told me that typical incandescent lighting, which is yellowish-white would have a colour temperature of 2,700K.  This is near enough for my purposes to 2,850K which is the temperature given for Tungsten in Lightroom.  However, Canon uses 3,200K as its setting for Tungsten light.  I refer to Canon, as I use Canon cameras.

Fluorescent is much more complex as its colour temperature can vary considerably due to the mixture of phosphors which the manufacturer has used inside the tube in order to achieve a given effect.  Here the range can be from 2,700K through to 6,500K.  This is supported by looking at, say, the Osram catalogue.

Lightroom gives the Fluorescent setting as 3,800K and Canon is a close match at 4,000K.  I find that, many Fluorescent light sources emit a greenish light and it is this which causes the greatest difficult in achieving a natural colour rendition.  It is interesting to note that Lightroom also a +21 Magenta tint for Fluorescent, clearly intended to counter this greenish hue.  The Osram web site tells me that Fluorescent bulbs are  available in three "light colours".  These are:

• warm white, below 3,300K
• neutral white, 3,300 - 5,000K; and
• daylight white, >5,000K.

Seeing these figures it is little wonder that I struggle with colour when shooting under Fluorescent light, due to the range of tubes available.

Looking in more detail at CFL's, I read on the Osram web site, that these are rated as being around 2,500 - 2,700K

Turning to the exercise, it is in two parts; the first asks you to compose a photograph in which both the interior lit by tungsten lamps and the exterior at dusk are both visible.  Three photographs are then to be taken with the WB set to Auto, daylight and tungsten.  The second part is to take photographs in two different interiors, setting WB to Auto and then to fluorescent.

Part 1:  Tungsten

As the light levels were very low, I have used ISO1600 throughout in order to enable me to hand hold the camera.

Auto WB

ISO 1600, f/4, 1/45 sec

The image appears pretty close to how I saw the scene, with a distinct orange / yellow cast arising from the tungsten light.  Clearly the overhead light is not tungsten as it does not give out that yellow light, but, looking at the bulbs, I cannot tell what they are, possibly CFL.

Daylight WB

ISO 1600, f/4, 1/45 sec

This has a distinct yellow cast, which is not surprising as the daylight setting in camera is 5,200K and the scene is lit by a tungsten light at, using the Canon setting, 3,200K.  3,200K is at the yellow end of the spectrum, hence the strong orange / yellow cast.  I would not recommend using this setting indoors.

Tungsten WB

ISO 1600, f/4, 1/45 sec

This photograph comes closest to the colours in the scene, so in this case the tungsten WB setting in camera is certainly the one to use.

In summary, the daylight WB setting is the least accurate, with the tungsten WB setting being the most accurate.  There is not much to choose between tungsten WB and Auto WB, the latter giving quite an acceptable rendition of the scene.

Part 2: Fluorescent

My choice for this was Jubilee Line station at Canary Wharf and the National Theatre on the South Bank.  I suspected that in both cases fluorescent lighting would be used, but could not be certain.

Canary Wharf Auto WB

ISO 3200, f/6.7, 1/30 sec

Auto WB appears to be coping with the lighting pretty well and this image appears to be reasonably accurate.

Canary Wharf Fluorescent WB

ISO 3200, f/4.5, 1/60 sec

To me, this looks a touch green, so the Auto WB setting has done this much better.  Examining the settings, the Auto WB had an extra +10 Magenta tint which can explain this.

Canary Wharf Daylight WB

ISO 3200, f/6.7,  1/30 sec

For comparison, I took a shot using daylight WB, and here the yellow / green hue is really apparent.

National Theatre Auto WB

ISO 1600, f/5.6, 1/15 sec

I really should have increased the ISO here, but I got away with a handheld shot, though braced, at 1/15 sec.  Again, I have found that the camera's Auto WB setting is coping pretty well with the lighting and has rendered a pretty reasonable result, though there is still just a bit of green visible.

National Theatre Fluorescent WB

ISO 1600, f/5.6, 1/15 sec

Here the green has gone pretty much entirely, so this is the more accurate result.

One thing that I have found in this exercise is that overall, Auto WB copes very well with a variety of conditions, and may need only a small tweak during post-processing.  Understanding the colour changes due to the colour temperature of different lighting helps with that task.  It is, of course, possible to set up a custom white balance in camera for each 'take', however this is time consuming, though there are accessories which provide help with this.

References

Wikipedia - Incandescent light bulb
Wikipedia - Fluorescent lamp
Philips lighting web site
Osram lighting web site
Canon EOS 5D Mark II and EOS 50D manuals

Exercise: Judging colour temperature 2

For the second part of this exercise, the objective is to take 3 images, this time varying each image by altering the in-camera setting, so that for each set, one is taken with Auto WB, another with the daylight WB and the third using the shade WB setting.

For this I used the same setup as for part 1 of this exercise, with Gwideon the Griffin as the patient model.

Sun: Left to right AWB, Daylight, Shade

As could be expected, there is very little difference between the AWB and Daylight setting as these were taken around midday, however there is a big difference for the Shade setting.  Here it is not faithful to the colour of the scene at that time.

Shade: Left to right AWB, Daylight, Shade

This time, taken in full shade, I find that the AWB setting is too blue and my preference is for the Daylight setting.  This has warmed up the image just enough to make it pleasing.  The Shade setting produces an image which is far to orange as the natural colour of Gwideon is grey with a touch of green moss.

Evening: Left to right AWB, Daylight, Shade

I expected a more orange tint in the evening and found that the AWB and daylight settings were not giving me what I wanted, or how I felt were representative of the scene.  The Shade setting brought in the yellow/orange colour which I feel is more representative here.

Taking this to a different situation, I took another sequence using these settings, this time some of my neighbours' houses were the subject.  This was taken about 7 in the morning in sunshine.

Morning in Bradford Street: Top to bottom, AWB, Daylight, Shade

In this case, my preference is for the image with the Daylight setting (in the centre) as this seems to give both that morning glow without going over the top as the image with Shade WB.  The AWB image is rather too neutral.

The importance of understanding colour temperature and judging how this will affect the final image is the key lesson to be learnt here.  There are two ways of looking at this:

• use the manual in-camera settings to give the best representation of the scene or the desired effect at the time of shooting; or
• shoot RAW at AWB and adjust in the RAW editor.

There are benefits to both.  The main difficulty with the first option is seeing whether the chosen setting is giving you the desired effect.  I find that using the screen on the back of the camera is sometimes difficult depending on conditions, so would not use this to make such judgments unless working, in say a studio.

Strong colour casts can be introduced by adjusting White Balance, and these must be considered as part of the creative input into the overall composition of an image.

My preference is always to shoot RAW as this captures all the information I need and I can then adjust using my preferred RAW editor, Lightroom.

Exercise: Judging colour temperature 1

This section looks at colour temperature and being able to recognise colour changes throughout the day.  It would be very easy to get caught up in the science, but for practical purposes, ie to help me appreciate the colour of different light sources and their impact on the image, all one really needs to know are some of the basics.

First of all, I would like to illustrate this with a single image.  This I took in the City of London in late afternoon a couple of weeks ago and I felt it really illustrates the difference between colour temperature in the shade and in bright sunlight.

ISO 400, f/6.7, 1/45 sec

The differences between shade and sunlight are very marked, considering that the stonework is a consistent colour throughout.  I used auto WB for this shot as I wanted both the sunlight and shade to be treated equally.  Here the stonework which is in the shade has a blue colour and this is very much attributed to the almost cloudless blue sky, which I can see in my images taken of other buildings adjacent to this at the same time.  The warm colour of the sunlight is really shown up in this image.

One of the benefits of shooting in RAW is that all information available at the time of recording the image is preserved and not altered in any way, so that it is then possible to alter the white balance of a photograph if the "as shot" does not look right.

The original was shown in Lightroom as being shot at 4900 Kelvin (K).  I then altered this in Lightroom, creating 3 further images, and these are shown above with the following settings, left to right:

• Daylight, 5500 K;
• Cloudy, 6500 K; and
• Shade, 7500 K

To me, the most pleasing colour balance is that described as shade, where the "cold" blueness of the stonework is "warmed" and there is less of a contrast between that and the sunlight flooding in at the back.

There are very many charts and other diagrams available in books and on the Internet, in particular from light bulb manufacturers, so I am not reproducing any of these here.  A summary of the science is that the temperature, expressed in degrees Kelvin (K), is recorded for the colour that an object would glow at if heated to that temperature.  An objected heated to give a red to orange glow would be at approximately 1,000 to 3,000 K.  Heating the object further until it emits a white glow, will record a temperature of 5,500 K.  Applying further heat, the object will take on an increasing blue colour, in the range of 6,000 K to 10,000 K.

In photographic terms, therefore I would expect the following:

• Midday sun is generally white with a temperature of 5,500 K as all the wavelengths making up light can be seen;
• Blue sky goes up to around 10,000 K
• Shade under a clear sky will reflect a large amount of blue and therefore will be between 7,000 and 8,000 K;
• Cloudy sky will be around 6,500 K;
• A fine morning or evening sun will be around 3,500 K; and
• Sunrise / sunset will be around 2,500K

Particularly in the morning and evening, at sunrise and sunset, atmospheric conditions will affect the colour and give a tint, due to diffraction of particles causing the short blue wavelengths to scatter, leaving the longer wavelengths.

Moving on to the exercise itself, the objective was to photograph a neutral coloured object in full sun in the middle of the day, in shadow at the same time and then towards the end of the day.  All need to be shot using the daylight WB setting.  

This is where I noted differences between the interpretation of settings in camera and those generally accepted and seen in Lightroom.  For the Canon EOS 5D II the following settings are given:

• Auto - 3000-7000;
• Daylight - 5200;
• Cloudy - 6000; and
• Shade - 7000

Left to Right:  Sun, Shade, early Evening.

My garden does not see much sun in the late evening, so I chose to take the last image in early evening, where the light was already tending towards yellow / orange.  Not the best of sets, but it does illustrate the point, with the shade being a bluer colour than sunlight.  

One of the learning points which I have noted during this and the following exercises, is that the eye sees colour differently to that which is recorded on the sensor, so the blueness in shade, is not always apparent.  Knowing what to expect in different situations then enables me to "see" these colours and make use of them compositionally.