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The disclosure gap, stated first
Plant care data is published in PAR - photosynthetically active radiation, measured at a depth. Aquarium Co-Op publishes Anubias Nana Petite as wanting 10-20 PAR. That is a useful, specific figure.
No nano light manufacturer publishes PAR at any depth. Not Fluval, whose Plant 3.0 Nano publishes wattage, spectrum, IP rating and beam angle but no PAR. Not anyone else in this class. So the buyer is given a plant requirement in one unit and a fixture specification in another, with no conversion between them.
We record that absence in the specification table of both products below rather than estimating a figure. It is the single biggest reason this category is hard to shop for on evidence.
How to choose without PAR
Match the fixture class to the plant class, not the number. Any nano LED sold for planted tanks will clear the 10-20 PAR that low-light rhizome plants want. The question is only whether you need more, and you need more only if you are growing a carpet or demanding stem plants - which in a low-tech tank you should not be.
Prefer a programmable photoperiod over raw output. A controlled eight-hour photoperiod is the best algae control that exists and it costs nothing to run. More light with no schedule grows algae; less light on a strict schedule grows plants.
Check the physical fit. Nano fixtures mount over the glass, on a rim or on legs. A rimless tank and a rim-clamp fixture are not compatible, and this is a surprisingly common purchase mistake.
Consider what the kit already has. If you bought a Fluval Spec V, it already has 821 lumens at 7000 K bonded into the lid, which is enough for every plant this site recommends. Buying a second light for it is spending money on a problem you do not have.
The color temperature question
The Spec V is 7000 K, the Flex 9 is 7500 K, and both are in the daylight range that grows plants and renders fish color naturally. Below about 5000 K a tank looks yellow; above about 10,000 K it looks cold and blue.
Where a fixture gives you independent channels - the Plant 3.0 Nano publishes six band waves with independent color control - the useful move is turning blue down. Blue drives algae growth hardest, and reducing it is free algae control that costs you almost nothing in plant growth.
Buy a timer before you buy a light
A five-dollar mechanical outlet timer is the highest-return purchase in this entire hub. Eight hours, every day, unvarying. The single most common cause of algae in a nano tank is a light left on because the tank looks nice lit, and no fixture solves that.
How long, and how much
Eight hours a day. Not twelve, not “while I am home”. If you have algae and otherwise healthy plants, cut to six for a fortnight before changing anything else.
A siesta split works - four hours on, three off, four on - and suits people who want the tank lit morning and evening. Plants do not mind; algae, which ramps up more slowly, is disadvantaged by the interruption.
Never in direct sunlight. A windowsill tank gets more light than any fixture you can buy, uncontrolled, and it will be an algae farm.
What we cannot tell you
What PAR either of these delivers at your substrate. Nobody publishes it, we have no meter, and estimating it from wattage across different LED densities and beam angles would be a guess dressed up as arithmetic. Where we cannot compute something, we say so rather than filling the gap.
