John wrote:
"Halogen lamps are incandescent lamps, with the only difference being that the addition of a halogen in the gas surrounding the filament permits the filament to operate at a higher temperature with reasonable life. (The higher temperature mandates the high-silica tube and the reduced gas volume that's typical.) The higher temperature theoretically at least provides somewhat more intensity at short wavelengths, and hence gives a higher "color temperature," while at the same time giving slightly more light across the longer wavelengths - hence a somehat "brighter" light. Halogen task lights can be "too bright" for some people if applied without some care, but problems with proper application are not materially different than for older incandescents."

While my understanding of them is broadly similar, it may be that some other information is relevant; it's been a while since I was seriously into the technical details so feel free to correct my misapprehensions.

There are two or three differences between quartz halogen (as they're often called here) lamps and the routine incandescents when used in routine domestic lighting.

1 The higher temperature (both degrees Celsius and 'colour'; the latter implies better approximation of flesh tones when using "daylight" colour film indoors) means they not only emit more light across the spectrum (including the longer wavelengths John mentioned) but also the shorter wavelengths. This means their UV output is a bit higher and not all of it is absorbed by the glass envelope. Most such lamps used in Oz domestic situations are housed in a reflective housing about 40mm diameter. If using them for reading lamps rather than area lighting or ceiling-mounted task lighting, the routine advice is to use the versions that have a glass pane between the bulb and the user. The pane absorbs the UV.

2 Most 'older' incandescents used in reading lamps and task lighting have a bulb that is at least 50mm in diameter; many people prefer 'pearl' bulbs as they diffuse the light so it appears to be emanating from the full diameter of the bulb, but even 'clear' bulbs will have a filament that is almost 20mm long emitting light from its full extent. Both these characteristics make close work more or less shadow-free. The reflective housing of most quartz halogen bulbs used in similar situations is usually not smoothly parabolic but is facetted. This may have been the cause of the multiple shadows in her close work that frustrated Bee.

Cheers, Rowan