What happened to that lamp? In addition to one knob (the one on the power switch) being mismatched to the other one, the diffuser screen is missing. Did whomever had this lamp before you accidentally break the screen? That's all that stands between you and having a lamp that will work the way its maker intended, unless the bulb is also broken or burned out. Replacements should be easy to find; I think this lamp uses a standard incandescent Edison-base bulb, the kind that's being phased out in the US (in fact has been phased out, as of January 1 this year) in favor of energy-efficient LED and CCFL bulbs. It might not be a bad idea to replace the original bulb in your lamp with an energy-efficient one, although standard bulbs are still available, albeit in short supply.
Replacing the original bulb with a CCFL or LED one will also give you one less bulb to replace for the next few years, as these bulbs can last ten years or more. On Insignia's website (
www.insigniaproducts.com), they advertise a bulb that will last 20+ years; this is probably an LED type, as I don't see CCFLs lasting quite that long. I have a CCFL bulb in a table lamp here; the bulb must be over five years old and still works, although it flickers every once in a while when I turn on the lamp at sundown, so it may well be reaching the end of its useful life. I had a CCFL in my other table lamp; that bulb burned out after five years or so. Both bulbs have the "GE" logo on the base, but I'm sure they were not made by the original General Electric Company, which for years had a bulb factory in suburban Cleveland. Chances are better than even that these "GE" branded CCFLs are made offshore, like everything else these days. Grrrr.