Some time ago, I bought an Expodisc to calibrate the White Balance setting on my camera. It costs me about AUD$100 and I have never put it to good use before. It is one of those things that I felt on hindsight I shouldn't have bought. Tonight, I learned otherwise.
I have taken some pictures recently with a set of Bunning's (non-pro) spotlight, which uses halogen bulb. Using the closest white balance preset of "tungsten" on my camera, I felt that the pictures I had taken were a little bit too warm.
Tonight I did some comparison shots. Both pictures shown here were taken with the same settings, except for the white balance. The first picture was taken with the white balance set to "tungsten", to match the lighting. The second was pre-calibrated using the Expodisc. As you can see, the second pictures gives a more accurate white balance. To be precise, the first picture has a colour temperature of 2950 Kelvin. The second was 2900 Kelvin; a difference of only 50 Kelvin.