Lumens are not a meaningful measure of brightness for a light like that. Lumens measure how bright a light looks to the human eye - which views yellow and green light as "the most bright". Since your light mostly lacks those wavelengths, it will measure as "dim" even though it is not.

A 28 watt LED grow light will probably be enough for one small plant that needs low or medium light levels.

Considering the true watt, Par value, and coverage. I am growing lettuce under a full spectrum LED. True 135 watt, about 500 μmols. the coverge is almost 2.5x2.5 I hang little high.

For a small plant, a 28 watt LED is okay. For other veg r flower, I suggest take a little powerful light.