Ok... Next would be suggesting some sort of control
Amazon.com: NICREW Aquarium LED Light Dimmer, Easy Plug Dimmer Switch for 12 and 24-Volt LED Strip : Pet Supplies
www.amazon.com
Now rough calc us that the 72" draws about 6A meaning you are at the borderline of the above manual dimmer specs (6 amps).
So use 2 dim to taste and what the plants tell you.
Buy Oznium LED Dimmer Knob with Rotary Control Switch - pwm dimming Control for 12 Volt LEDs, dim up to 8 amps at 12V: car Automotive, Low Voltage Under Cabinet Lights: Bulbs - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
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Branswork makes a plug/ play timer- dimmer but ??? if it is compatible e/ the 72"
8 amps but need to diy a bunch