It really depends on the species you work with (and possibly also other factors, like the flask you are using, the agitation, etc.). But my first guess is: start with 45 μE m−2 s−1 and once the culture becomes denser, turn up the lights gradually. It is not unusual that too much light can overwhelm a culture.

I am growing Nannochloropsis Limnetica (I re-cultured them 3 times at 45 before growing in high light and when it became denser at O.D. 1, I transferred it to high light 100 but it suddenly died).

As far as I know, cells don’t “suddenly die” at high light. Could it be something else? Sorry, I am really guessing here: if you split your culture and wrap one flask in aluminum foil and place it at the same place like the other: will it die as well?

Thanks for your answer.

I will try.

But another thing I tried also as the incubator that I am growing in does not contain carbon dioxide and the light intensity is 45 but I split the culture into two flasks then I put one in the infors with CO2 2% and 100 micromole light and the other in CO2 0.2% and 100 also but I found both of them died, from this I thought the reason is light.

but I will try to cover one of them with foil to see if the reason is light or not.