Friday, 2 September 2011

Tungsten and Fluorescent Lighting 2

The exercise here was to look at 2 different types of fluorescent lighting and compare the colours. As I has already looked at fluorescent lighting in the earlier part of the exercise I thought it was useful to compare the fluorescent lighting we have (CFL), with the other lighting we have which consists of the small halogen bulbs. These give a very intense point light, and again come a ceiling fittings or as single reading lamps. The light appears a very bright white to the eye.

A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle  which increases the lifetime of the filament and prevents darkening of the bulb by redepositing tungsten from the inside of the bulb back onto the filament. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life. The higher operating temperature results in light of a higher color temperature. This, in turn, gives it a higher luminous efficacy (10–30 lm/W). Because of their smaller size, halogen lamps can advantageously be used with optical systems that are more efficient in how they cast emitted light. (Wikipaedia)

Trial 1.

These were taken in my study, which has a single CFL light as the ceiling fitting. It is not very bright and takes a long time to 'warm up' to full brightness. The light appears yellowish to the eye.

I chose a still life of blue and greenish objects set on a blue cloth. The colours were possibly too similar, but I wanted to see how the camera would cope with differentiating them.


The AWB setting actually coped surprisingly well. The cat is possibly a bit too creamy, and the owl a little green but the other colours are accurate.


Oddly enough, the white balance setting for 'incandescent' , which I assume was developed for using with tungsten bulbs, worked reasonably well in the setting, although the owl is too green. It had not been at all effective in the previous setting in the living room with a different type of CFL bulbs. (see previous post).

2500K setting

My camera does not give any specific settings for fluorescent lighting, but it does give the option to set the white balance to a specific colour temperature. The packaging for the bulb gave the colour temperature as 2500K so I set the white balance to reflect this. This is the most successful so far, The cat is now a little too white (possibly slightly overexposed), but all else is correct.

Set WB

Here I used the setting where I had set the white point. This is the best of all, with accurate colours. (the cat is still possibly slightly overexposed).

Trial 2.

For this trial I moved to the kitchen where the ceiling fitting has the small halogen bulbs that are very common now. I used the same still life.


AWB has given a very poor rendition of the colours. The blue cloth looks pale purple, and the owl is an odd grey-green.


The incandescent setting, which should , in  theory, work, is rather better, The owl is slightly too blue, but the colours are generally acceptable.


 For comparison I also tried the 2500K setting that had worked well in the study with the CFL bulbs. Here everything definitely has a much too blue cast.

Set WB

The set white balance has been less successful here, again everything looks too blue, and the brown edge of the unit that just shows has lost all warmth.

These exercises clearly show  how important it is to consider white balance when taking photographs with artificial light.  The CFL bulbs do seem to be slightly more 'forgiving' although to the eye the look both dim and slightly orange. The halogen bulbs (although looking neutral to the eye) can give some very odd effects! It is clear that I need to think about white balance is taking pictures in the kitchen.

Or there is an alternative option:

Take the best option (the one using the incandescent white balance setting) and alter it in Lightroom (or PSE). The advantage of shooting in RAW. This has ended up with the best colours of all.

Learning Points:
  • don't always rely on AWB
  • think about the type of light, and compensate accordingly
  • not all CFL's give the same effect
  • you may need to alter further in post-processing to get the correct colours

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