I am using the BESTVA 3000W grow light, and the distance between the light and the plants is about 25–30 cm.(The PPFD value is measured at 1,500–1,800

That lux meter will help you best choose how to set them up in an array, too... this requires a little fine-tuning to figure out how much you can give without damaging the plants... find correct hanging distance, then work on best alignment of array.

First, that's not how PPFD works. An area of coverage in m^2 would be needed for that "PPFD" value to make any sense. PPFD is umol/s of PAR per m^2. No area mentioned, no rational sense can be made from it. Want to understand that better? Read up on Daily Light Integral (DLI) to get the gist. PPFD without hours of operation is equally incomplete information. DLI is what matters. I doubt these are licensed lm301 diodes, so it's probably a low efficacy light, which means more heat, less light produced per watt/s. It's 300w of low efficacy led diodes. While not a QB, it can be treated like one as far as hanging distance due to poor distirubtion of diodes. 16-24" is probably a better distance. You want to cover 35-40w/sq ft so they'll probably cover a bit less than 8 sq ft each. This would be for 12hour operation, if growing autoflowers or in 18h operation vege, can cover proportionally more area or reduce wattage and cover the area maxed out by 12 hour operation... ~27w/sq ft would be a good initial target for 18-hour operation. If growing photoperiods, remember you are limited by 12-hour operation requirements. spec sheet on amazon roughly agrees - 4x2 .. i doubt it can fully cover 4' and 2' but close enough. Use that lux meter. it is proportional to intensity and therefore a good tool. Measure in center and that value is "100%." MEasur same distance from light at various points - like corners and edges. Without sacrificing overall average of these readings, reduce difference from center to edges/corners by increasingn hanging height. Based on diode distribution, this is gonna be between 16-24". Local temps, RH and atmospheric CO2 will impact exactly what you can give.