undesired screening of my cells under fluorescence microscope

[bidin ozor]

when I used blue filter, although I did not stain my cells, I see my cells like in attached photograph

I am lost.... Is there any explanation of this???

[CharonY]

I cannot really see much in the image and without detailed settings with regards to type of microscope, filter sets etc. it will just be speculation. However, is there stray light or was bright field illumination on?