Sunday, 9 June 2013

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.


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

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