Lamp Type: You need full spectrum visible light, which emits all the colors from red to violet, to illuminate art work. However, you do not need or want any ultraviolet or infrared because they both harm color pigments evven though they are invisible. While possible, this is very difficult to achieve in practice as most lights bleed some ultraviolet or infrared.

It may be important to understand that the spectrum of light a bulb emits can not be widened with filters. If a bulb does not provide the colors blue or violet - but your print does, its blue or violet parts will be less than what you or the photographer expected.

Amount of Light: You need enough light to be thrilled with the artwork, but not so much that the art is harmed by the light. Artwork Pigments can be quickly damaged above 150 lux (at the artwork surface), primarily by ultraviolet light (UV). It is very important that the art always be protected from the ultraviolet energy of direct sunlight. Fifty (50) to 100 lux should be enough light to pleasantly view most photographs. 100 lux is roughly the light outside on a "very dark overcast day"; 50 lux is roughly the amount of light in a "family living room" according to Wikipedia.

Spread of Light: it is important to have the light spread the right amount. Too narrow and part of the artwork is unlit; slightly too wide is preferable.

Bare or Diffused: Halogen lamps generally have harsh edges at the limits of the light footprint and distracting patterns from the bulb in the center of the light pool. Diffusers can soften both of these problems. Modern museums use diffusers on their lights.

Light Placement: Lights need to be placed at an angle to the art work, generally from above on the ceiling. Less than thirty (30) degrees can distract your eyes by putting too much light on the matt or frame. More than sixty (60) degrees and you'll see reflections of the light source itself. (90 degrees will reflect right back in your eyes.) Which is related to --

Reflections: If you have a solid black wall opposite and the photography work and lights are at just the right angle, shiny glass can look great. However, white walls with other interesting art work may face the work you intend to light so you'll typically need to choose glare-free glass or acrylic to protect your work and minimize distracting reflections. Before you choose shiny glass you might hold up a mirror or normal glass in the location where you intend to hang the work so you can see what may distract your eyes from the finished art work.

It may be light streaming in from a window across the room or even your own reflection that is distracting. Glare reduction acrylic really does remove those distractions, but the placement of the lighting can still cause problems. It is possible to tilt the work a few degrees back at the top so the reflections are from the top of the opposing walls and the ceiling, but not everyone likes this effect and you have to be careful that ceiling lighting is not reflected.

For decades...