What's up with green desk lamps?
Green has a calming effect on one's mood, so maybe a green desk lamp neutralizes the effects of a stressful day at your work desk. Just guessing.
Can one use 20W fluorescent tube lamps as a substitute to 40W lamps?
Yes they will work if they fit the fixture.... They will only draw the 20 watts they need to operate, so No, you will not blow the 20W lamps.... Ensure however that the lamps you will be using are rated for 220 volt operation... I am guessing you are...
where can i buy a really cheap desk lamp?
At Target I got a clip-on lamp for $2. Holds a 40-watt bulb and works great. And it's cute. Target, Wal-Mart, K-Mart have a lot of cheap lamps.. especially for dorms and back-to-school supplies.