The use of evive was to control the intensity/brightness of power LED. evive's power module has a variable voltage power output (buck) ranging from 1.25V to 30V. We used a 12V (or a 9V) battery to power the LED, but when you place it in front of your mobile camera via the "subject" on a glass slide, you need to adjust the "incoming light". We have adjusted the voltage across the LED using evive.
(Mobile camera also has inbuilt light intensity/exposure adjustment, but the main use was to control the light on the subject for eg. some insect/worms may be very dark while other can be translucent (like wing of a fly) )