What ambient lighting is appropriate for a room where photos are edited and proofed/printed?

Assuming monitor(s) are correctly calibrated and print viewing is done in a viewing box with its own light source, what should the room lighting be? With no lighting at all I think most people find the contrast between monitor and the rest of the room much too harsh (and its a bit depressing), but what kind of lighting is appropriate? I currently have a 150W 6500K bulb which is very bright and causes a lot of reflection from my screen.

Would a dimmer bulb with the same (daylight) temperature be appropriate?

Answer

You don't need a dimmer bulb, you just need to disperse it properly so that it is more evenly distributed throughout the room. Rather than placing the bulb where it is shining directly on your monitor, place it in a fixture and bounce it off the neutrally colored walls and/or ceiling so the light is fairly uniform throughout the room.

The standard for viewing photos on a monitor is D50 (broad spectrum light with all of the components, including UV, carefully controlled and centered on 5000K). For LCD monitors the intensity of the ambient light as measured at the center of the screen should be 55 Lux. The monitor should also be calibrated to D50. Recommended maximum brightness with an LCD monitor is 120 cd/mm². For a CRT it is 100 cd/mm².

There are many in the graphics industry that prefer to use D65, which is centered on 6500K, for monitors. This is perfectly acceptable as long as the monitor and the ambient lighting match. However, care must be taken not to allow the 6500K ambient light to affect the perception of the D50 light source illuminating prints in your print viewing booth. In the case of a small print viewing box, you would need to turn off any non D50 lighting when critically evaluating photo prints. Otherwise you risk metameric failure.

Metamerism is when two objects render different spectral power distributions yet visually match under a certain lighting/viewing condition, but not under another. Two objects that visually match under at least one lighting condition are called a metameric pair. When two objects match under one light source/viewing condition but not under another, the resulting condition is called metameric failure.