In my experience for cell migration the cells definitely prefer low power
for a long time. I have never seemed to find the time to systematically
measure this but I should. Cell migration is very sensitive to light so it
is a good assay to test it with. You can also measure the migration rates
with brightfield imaging for comparisons with no fluorescence light applied.

I was once using a Fluoview 300 at 0.1% power to measure protrusion rates
with 20s intervals for imaging and when I went up to 0.2% the lamellipodia
immediately started to retract. I also know when using TIRF illumination
where on the lower 100 nm of the cell is exposed to light the cells are much
more dynamic and motile.

I would definitely go with 100 ms at 1%.

I let you know if I get some more concrete data on this.

Sincerely,

Claire
McGill Imaging Facility