Basic camera coverage of a computer room would typically include the entrance and exit doors. The objective here is to provide accountability (in conjunction with any access control system used) for people entering and exiting the room. Facilities who process credit cards would generally want this to comply with Payment Card Industry (PCI) standards.
Some of my clients also want coverage down the front and back of each row of server racks. The objective here is to observe who has been working on what equipment and when. This is especially common in colocation ("colo") sites where multiple users are sharing a computer room. I have also had clients request coverage of their "Emergency Power Off" (EPO) buttons. If anyone presses this button, they want to be able to positively identify them.
I have found that computer/data center security is one area where owners are not particularly budget concious. Usually, the cost of security/surveillance equipment is chump change compared to what other systems in the data center cost. Also, the cost of downtime on data centers can easily run into the millions of dollars per day for many organizations, so they feel that anything that can be done to prevent this is money well spent.
I have done a number of surveillance centers that use Arecont panoramic cameras or Axis/Vivotek Fisheye cameras for the monitoring of the aisles. They usually use high res cameras for the entrances to monitor who comes in and goes out, and then use the fisheye/panoramic cameras to monitor where they go from there. If tied to an access control system, they can link the video of them entering with the badge read at the door.
As for your other questions:
- It was lit only when people were inside to save power and heat. One had their lights programmed to go off automatically once everyone was badged out of the area. The other had motion sensors.
- Yes budget was a concern, but it can be done economically.