Home UVB light treatment without Doctor/Derm

[ricoghardforth]

I've suffered from mild plaque psoriasis for the last ten years.  I started with it in and around my ears and it progressed to a patch on left knee, a patch on my  right shin and has been on a off my elbows ever since. I've also a small patch on my back which I can't reach.  I've been using Dovonex on and off and it don't appear to reduce the size of the patch's at all just maybe helps the thickness of the white scales and I try to keep the patchs to just a red mark by having long soaks in the bath where I cover the patches with aqueous cream before I gently rub off the white scaly skin build up using the tips of my fingers.  I've also been getting small patches on my eyelids for last couple of years and have been using a mild 1% steroid cream on them.    

I've just bought a uvb lamp off ebay from Poland with a Genuine PHILIPS PL-S 9W/01 G23 bulb which i'm hoping to use it to reduce the size of the  the patches on my legs and elbows.
However the instructions are very basic as you can see from my pics.  It says increase the dosage by 8 seconds per treatment and for the final dosage it must be recommended by a doctor based on skin reaction.  Which doesn't help as I wasn't going to go to the doctors as this treatment has not been prescribed by them.  So can any one help with at what point to you stop increasing the exposure time and at what point do you stop or start to decrease the expose times or do you just increase the duration between treatments.   Thank-you.