The lamp is dimmer than I expected
Output, and why a Dimpsy lamp reads darker than an equivalent bulb.
The short answer
It is dimmer on purpose at the warm end, and the numbers are honest: 480 lumens for One, 620 for Tall, 540 for Halo. A 60W-equivalent bulb is around 800.
Why it still lights a room
The beam is controlled rather than scattered. A lamp that throws 800 lumens at the ceiling puts less on your desk than one that throws 480 at the desk.
If it is genuinely too dark
Check the schedule. If the app has calibrated to a high sensitivity it will have lowered the evening curve. You can override that from the Calibration screen.