You can use the LED type lamps, or measure the irradiance in specific points of their culture room and put the treatments exactly in the same irradiance

Thanks. I have tried the second option but the problem is that when you go back and measure the irradiance the next day it is different as some of the bulbs would have gone dim (use 12 lamps).

You may divide your experiments on small plots, on which it is easier to control the variations in irradiance. But think about the possibility of using LED cost cheaper and have better quality when compared to common bulbs

What if you put your flasks on plate equiped with a rotor that turn slowly ?

I think if you want only culture algae you can put the lamp along the shelf and shake the flasks gently , rotational movements, once a day.

When you have to perform the test you have to count under the microscope, for example, the algal cells and dilute the algae up to a note concentration.

when you start with test you have to measure and know the lux and temperature, both constant for all time of test, so you may have the instrument, luxmeter, to know under which lux you put your flasks, perhaps you can put more lamps along the shelf.

Personally I perform test in a refrigerated thermostat (at temperature and lux controlled and constant) and the culture in a room.

Thanks. If I may ask what type of lamp do u use and how long does it take before you replace them

sorry for my slow answer... I use old long neon for the culturing, and I don't know the exact name of the lamps in the thermostat box because it was already set up with them in.

The algal test requires 10000 lux form the sides or 6000 lux from the bottom.

Thanks for the information

I also use a T4 fluorescent lamp(8 in set, build up on stele), with additional reflecting foil above. I get even 12k lux at the bottom of shaker. I designed the stele very regulative with possibility of turning off selected lamps and setting any height I need. Due to that I can easily increase the light intensity by using all lamps and decrease it by increasing height. That allow me to obtain the uniformity of lighting at enough, not exciding 10%, level. With only half of lamps turned on I get much higher unequality (25-30%) of lighting even if average level is sufficient for the test approx. 6k lx.

And as it was mentioned earlier a lot of unequality in light distribution can be solved by frequent changing of flasks position during the test.

Thanks. I have been doing that presently.