White Balance
Light is different colours. We don’t notice it, because our brains give what we see the colour it “should” have, but cameras aren’t so good at it. The colour of light is measured by its colour temperature, which is measured in degrees Kelvin. The lower the colour temperature, the redder the tint. Candlelight is about 2000º Kelvin. Sunlight and flash is around 5,500º Kelvin, and the light from a blue sky can be as high as 10,000º. So, light bulbs give our an orange light, sunlight is nice and white, and fluorescent tubes can be any number of colours, although they are usually greenish. Digital cameras, however, have it easier than traditional film cameras.

A quick note about white balance in film cameras: it all depends on the film. You’ll need to buy film specifically made for particular lighting situations. If you use the wrong film, you’ll end up with an unusual colour cast on your photos. This is because the films are designed to favour different colour temperatures in order to prevent a cast of one particular colour. For example, film designed for tungsten lights (such as regular light bulbs) is designed to tone down the orange colours because tungsten bulbs give out so much orange. Use it indoors with regular light bulbs and you’ll get nice colours, but if you use it in an office where it’s mainly fluorescent lights, and you’ll get a distinct greenish blue tint to your photos, because tungsten film is designed for a different colour temperature. And those harsh orange-yellow streetlights are absolutely terrible, because they don’t give out light across the entire spectrum. They only give out light at the yellow-orange region, so if you’ve got a blue object in the photo, it will pretty much turn out black no matter what. Because of this, film cameras have trouble if the light source is variable, or if you are going to be going from one area to another with different lighting conditions. About the best you can do is change the film, but this may mean sacrificing a number of frames to the photo gods. You could also use filters specifically designed to alter the tint of light, but this will cost you some light, perhaps one or two stops, depending on the filter.

On the other hand, digital cameras have a much easier job, because they don’t rely on film. The white balance on digital can be altered at any time. There’s no excuse for not having the correct white balance with a digital camera, it’s the easiest thing in the world to go into the menu and change it. For regular light bulbs, choose tungsten or incandescent. The other settings are pretty self explanatory. Use cloudy if you are outside and in the shade, such as under a tree. Also use cloudy if you are shooting a panorama (so your white balance doesn’t change between shots). If you aren’t sure what white balance setting to use, pick one, take a test shot and see how that looks. On some cameras, you can create your own white balance. You can also use a photo on the camera to set the white balance – it works like this: you take a photo of an 18% grey card (you can buy these at any decent camera shop) so that it fills the frame, and then you tell the camera to create a white balance setting that removes all colour from that photo. The exact method depends on the camera you are using.

Of course, if you are shooting in RAW, just ignore all this. Set your white balance to Auto and you can fix it later in Photoshop or your RAW editor.

A final note – the light from a flash (be it the camera’s inbuilt flash, a flash unit that slots into the hotshoe, or studio flash) is designed to have the same colour temperature as sunlight. So, using the daylight white balance will give fine results with flash, although it does mean things can get a bit tricky if you are using flash in a situation that has a different kind of lighting, such as fluorescent lights. In a situation like this, you may be able to put a gel over the front of the flash to make the light from the flash match the ambient light, and then adjust the camera's white balance to suit that particular colour temperature. For example, if you are in a location where the main lighting is tungsten and you decide to use your flash, you should put a orangevgel over your flash to tint it the same colour as the tungsten lights. Then you can set your white balance to "Tungsten" and the photo will look good. If you don't use the gel on the flash, the parts of the photo lit by the tungsten bulbs will look fine, but the parts lit by the flash will look too blue.