Lighting and weight

Adding lights or bigger lights is always a good thing, the light supply is the heart of the operation, after that you might want to check out if your getting the proper nutrition you might not be feeding them enough or you could add a supplement, but for a simple fix if your plants are typically healthy adding light is the way to go or a bigger light

Side lighting can also help a lot.

Well, if you provide 45 DLI on the whole surface you’ve got, the yield will be higher. To achieve this you need to install second lamp. Two lamps will make more even illumination. That’s the goal. Another important thing: how much DLI you can provide to the whole length of bud. You will always have fading illumination according to reverse square law. Surely you can’t hang the lamp too close to the canopy in order to give more light to the lower bud sites. But you can use it full power and hang relatively far away from the canopy. In this case lower sites will receive like two times less light than the top for example. If you go low power LED or dim it, you need to place it closer to the canopy in order to give enough light AT LEAST to the tops. The lower sites will get like four times less light. Don’t light stress the plant. Don’t go higher than 45-50 DLI, and you’ll definitely get more yield. Surely you will need to adjust feeding. More light - more nutrients needed. But some factors like VPD should be also taken into account. High VPD - lower EC, low VPD - higher EC. Good luck!

Light is certainly one important piece of getting the most from your grows but 400W should be sufficient.... My question concerns your nutes... when they go into flower, are you adding more P and K? A PK booster, for example? Those two nutrients are essential for targeting the buds, their growth and their density... It's also hard to overdose on them (but it IS possible so don't go TOO crazy)... I use, for example, General Hydroponics KoolBloom liquid from the first week of flowering to 2 weeks before harvest when I switch to KoolBloom dry formula. The liquid has an NPK of 0-10-10 and the dry has 2-45-28.... If you're growing in soil, one thing you can try, from the first time you give nutes to harvest, is to sprinkle 1 tablespoon of Langbeinite (NPK 0-0-22) on top of the soil once a month... this will also help avoid a calcium deficiency (or so I'm told by an old timer)... It's quite inexpensive and can be found either on Amazon or at a local garden center. So lights play a part - but only a PART... take a look at what else you can do to increase your yields... and good luck!