I used the big free lamp outside the sun!
It does have to be sunny but winter sun is fine. If you're using regular paper use cheap stuff, some of the more expensive ones have a coating which blocks the light. I put the pic on the clear perspex sheet, peeled off the protective layer on the photoez (VERY important, I messed up 2 sheets like that...) and put it shiny side down on the photo. Line it up, clip on the back board and check the alignment. Place in the sun for around 5-6 minutes and then place in water for at least 10 mins with a cover on it. You should be able to see your design faintly as a lighter green colour on the stencil when you take it from the exposure frame.
Once it's soaked gently scrub the image from the stencil with your fingers - a brush is too hard on the softened emulsion (guess how I know? ). Then dry it gently by pressing with a kitchen towel and leave in the sun to dry. I leave mine in the window.
Out of the 7 sheets I started with I have 4 good stencils and a couple of good smaller pieces. As with regular screenprinting there is a learning curve to it.
What I would suggest if you want to use your lamp is measure up your image and see if you can take a small strip off of one edge. Print off a simple design to use as a tester, something like a simple border. Set this up as one long strip and begin exposing it starting at 20 mins. After 20 mins cover up about an inch or 2 with a pice of card or similar. 5 minutes later move the covering piece so it is over the original part plus about the same amount again. Do this every 5 minutes until you reach the end of the strip, then wash out as above. As you would have done it in 5 minute intervals you can then tell how long you need to expose it with your lamp to get a good exposure. The early ones will more than likely wash out, the later ones will likely be over exposed and not wash out at all but somewhere in between will be a good exposure
Hope this helps!
PS: I'm not on much at the moment as my pc has died and the one I'm using now is a resurrection of an old machine that is barely running!