Paul sent me a link to a Wikipedia article, http://en.m.wikipedia.org/wiki/Kruithof_curve which is new to me. I was introduced to some other illumination terms such as correlated color temperature by the website donklipstein.com which has a wealth of info on lighting and LED lights.
Before CFL and LED lights, we were using incandescent lights which have a color temperature that is limited by the temperature of the tungsten filament. The manufacturer of the light determines what this temperature is by setting the amount of resistance of the filament so that the light has a reasonable lifetime and puts out enough light. The manufacturer could do little to change the color temperature of the light. All that has changed now that CFL and LED lights are being sold. These lights use phosphor to supply the light, and the phosphor can be changed to change the light’s color temperature. This change is just a matter of changing the chemicals used for the phosphor. With CFL and LED lights you can buy soft white which is similar to incandescent lights and you can buy bright white or daylight which is similar to sunlight. There may be other colors, but generally they are not seen in stores.
These changes to lighting have brought these physical lighting terms such as correlated color temperature and Kruithof Curves out of the language of specialists, and into more general use. But it may be a few years before the lighting industry gets to develop and use them in lighting design; at this time it seems the lighting industry is more oriented towards duplicating the incandescent light and saving a lot of energy.
There is a TV series now being shown on PBS, called Your Inner Fish. Episode 2 of the series is called Your Inner Reptile. They discussed the mammals that were in existence around 65 million years ago before the dinosaurs became extinct. These were small furry creatures that were nocturnal, they slept in their burrows during the day and came out at night to forage for food. After the dinosaurs became extinct the mammals started to come out during the daytime, but today we still retain some of those reptilian and early mammal characteristics in our genes. It seems to me that this may be why we like to sit around a campfire at night and enjoy its warm glow, and tell spooky stories. It may also explain why we like the warm white glow of candles and incandescent lights. There are many creatures out there in the forest that are just waiting to take a bite out of you, so keep the fire lit all night long, or they might actually bite you! :-O