light makes the alarm sound?

veritas alarm seems to get irritated by the cellar light the alarm and the celler flourecent fitting are not wired together because they run off seprate fuses it is a tamper fault ive had the alarm almost 11 years with never a problem ive got a keypad downstairs and upstairs the outside box flashes green red fast and it is flashing blue because i havent botherd to reset it and ive once seen tamper off then the tamper light come on but often dosent sound any ideas