Here's an example of the improvement that great lighting can make - as opposed to merely good lighting.
To allow a fine art photograph (or painting) to show its full range of luminous brilliance, delicate details and subtle colors - it needs carefully thought out lighting.
Bulb or Lamp Type:To illuminate art work you need complete light; the entire spectrum of visible light, which emits all the colors from red through violet. However, you do not need or want any invisible "light" from just outside the visual range, called ultraviolet or infrared, because they seriously harm color pigments even though you cannot see them. While it is possible to arrange this, it is very difficult to achieve in practice as most lights bleed some ultraviolet or infrared.
It may be important to understand that the range of colors a bulb emits cannot be widened with filters. If your bulb / lighting does not provide the full set of colors blue or violet - but your print does, its blue or violet parts will be less colorful and less color accurate than the print would appear in sunlight.
No lamp can match sunlight, but oddly matching sunlight may not provide the most pleasing color rendition due to a capability of our eyes called "chromatic adaptation." While difficult to believe, this means that different light color balances appear correct depending on the brightness of the room.
Xenon, Halogen and incandescent lamps allow you to most accurately see the colors in a print.
1. Xenon lamps provide the best colors, closest to sunlight, and use only a third the energy of Halogen, but are harder to find and can be more expensive. You are familiar with xenon since almost every camera flash now uses them. In automobiles, only BMW employs xenon bulbs.
2. LED bulbs now provide great white light, but they are very expensive. (An experiment with LED lighting at the Getty Museum showed no more harm to photographs than from Xenon lamps and about a quarter the energy costs. I expect LED is the lighting of the future.)
3. Halogen has a slight blue tint and is often too bright. Excessive brightness can be reduced by moving the lights farther from the work, or finding lower wattage halogen bulbs, dimming switches or neutral density filters.
4. Incandescent light (a traditional light bulb) is slightly yellow because it is weak in the blue-green part of the spectrum.
5. Most Fluorescent lamps do not give adequate color rendition, though some believe they are sufficient for viewing black and white photography. I suspect they give the white areas of a print a color cast. There are Fluorescents that claim to give "full-spectrum" "white light," but fluorescents can put out more than a little ultraviolet light; pigment-harming, and skin cancer causing, UV light. Worse, they physically contain the toxic liquid metal mercury making breakage more dangerous and disposal more work.
The CRI (Color rendition index) is a poor indicator of light value and can generally be ignored. It can roughly tell you how close to full white light a lamp gives. 100 is best, lower than 90 is lacking.
Xenon = Best
LED = Very good (expensive)
Halogen = Good
Incandescent = OK
Fluorescent = Avoid
Amount of Light:
You need enough light to be thrilled with your artwork, but not so much that your Art work is harmed by the light. Most photographic artwork pigments (silver halide or "giclee" from an ink jet printer) can be quickly damaged above 150 lux (at the artwork surface), primarily by ultraviolet light (UV).
It is very important that your 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. The National Gallery in London has a policy of lighting most paintings at 200 lux, with a yearly limit of 600,000 lux-hours.
You can measure the brightness with a light meter pointing at the bulb from the artwork surface on the wall.
As described above for Halogen blubs - you can reduce excessive brightness by moving the lights farther from the work, or finding low wattage bulbs. It is not common practice, but if you can't use other methods, you could also use neutral density filters - available at photography and science supply stores.
Spread of Light:
It is important to have the light spread the right amount. Too narrow and part of the artwork is unlit. If you have to choose between too wide or too narrow, I prefer slightly too wide so the frame is just barely lit.
Bare or Diffused:
Halogen lamps generally have harsh or sharp edges at the limits of the light footprint and distracting patterns from the bulb in the center of the light pool. Both of these distract from the artwork. Diffusers can soften both of these problems. Modern museums use diffusers on their lights.
Lights need to be placed at an angle to the art work, (because at 90 degrees it will reflect right back in your eyes). Generally that means lights are above the work from the ceiling. Less than thirty (30) degrees from directly above the work can distract your eyes by putting too much light on the matt or frame or wall. More than sixty (60) degrees and you begin to see reflections of the light source itself. Which is related to --
Reflections (Glare-free Glass?):
Do you need glare-free glass?
Normal shiny glass can look / work fabulously. But you need a solid black wall opposite the photography work and lights at just the right angle. (You also should wear dark clothes.)
Before you choose normal 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.
However, to protect your work and minimize distracting reflections when white walls with other interesting art work may face the work you intend to light - you'll typically need to choose glare-free glass or acrylic.
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 or reduce 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.
Now that your photographs are perfectly lighted . . .
"Lux" and "Footcandles" are measures of light intensity as perceived by a human eye.
One lux = light from a full moon overhead at tropical latitudes.
Direct sunlight is about 130,000 lux (overhead at noon), and drops to 32,000 lux when the sun is near the horizon (at sunset or sunrise).
One footcandle = 10.7 Lux
How to Mount and Frame a Fine Art Photograph