Aquarium Light PAR Is a Point Reading, Not a Tank

The reading said high light. The carpet still melted at the front corner.

Picture a reading taken dead centre, sensor on the substrate — a number that reads as solid high light on any published chart, and the reason an aquarium light par reading taken at that single point can tell you your Monte Carlo should be thriving while the front corners of the same tank get considerably less. The evidence gathered here gives no conversion from a centre reading to a corner one, and no documented case of a carpet failing after a buyer hit a target PAR number.

Built from published specs, hobbyist builds and forum-documented results, with sources named in the text. Links may earn a commission, which has no bearing on what gets recommended.

That gap is the whole problem. PAR — properly PPFD, counting photons in the 400–700 nm band landing on a square metre each second, as Aquarium Co-Op sets it out — is a point measurement, not a property of a tank. Aquascape Guide notes that published PAR tables are taken at 100% intensity directly beneath the fixture, which is the single most favourable spot in the water column. Every other litre gets less.

This piece is for anyone who has a PAR figure in hand, from a chart or a borrowed meter, and needs to know what their plants actually receive. It treats PAR as two things the charts leave out: depth and photoperiod. By the end you will be able to take any published number, discount it for measurement point and mounting height, convert it to a daily total, and say whether the fixture you own can carpet the front corners or only the middle.

Sunken Treasure Aquatics puts it bluntly: water parameters, substrate colour and mounting height all change what reaches the bed. A published figure is a starting point.

The short version

• The pick: VIPARSPECTRA 165W, for it is the right answer for a deep reef tank where corals near the sand bed still need usable PAR, since it is engineered around PAR output across a 24x24 in footprint and hangs above the rim rather than clipping to it.
• Also worth it: Lominie, for it is the right answer for a nano tank or a refugium where the fixture must reach over an odd rim and the beam angle needs narrowing to concentrate PAR at depth.
• How this was decided: published specifications and buyer reports across 5 products, compared below.

Which PAR number are you holding? Reconciling the 10-20 and 75-100 scales

Two published scales disagree by up to sevenfold, and nobody labels which one a chart figure belongs to. Aquarium Co-Op puts low light at 10-20 PAR, medium at 20-35, high at 40-50 and above, with CO2 described as typically a necessity in that band or algae takes over. Buce Plant cites a community guideline of 75-100 μmols for low-light-demanding plants, roughly 150 for medium and 200-plus for high. Same units. Same plants. Three to seven times apart.

No source reconciles the two scales, and neither page states the measurement depth or position its numbers refer to. Aquarium Co-Op's low-light band is described in terms of low-tech plants such as anubias and cryptocoryne with no CO2 injection; Buce Plant pairs its figures with a recommended photoperiod of about 8 hours. Aqueon, by contrast, recommends 12 hours for planted tanks and 8-10 for tanks without live plants. An 8-hour day at 150 μmols and a 12-hour day at 20 PAR at the substrate are not the same prescription, and they are not meant to be.

Check what the number is attached to, not what it says

No source in this set explains how to map one scale onto the other, so the safest move is to note which guide a figure came from. What is documented is that published tables are typically measured at 100% intensity directly under the light, the single most favourable point in the tank.

Instruments differ too. The Chihiros figures below came from a Samsung S22 Ultra running Photone, not a calibrated quantum meter, while Aquarium Co-Op's own figures were taken in a 65-gallon aquarium at 100% brightness. No source addresses whether phone-app readings are comparable to meter readings. Aquarium Co-Op's own position is that chasing specific PAR values matters less than knowing your plants' needs and watching growth over time.

Measured falloff in the published readings

Aquascape Guide's readings for a Chihiros WRGB II 90 Pro, a 100 W fixture, give 955 PAR at 3 inches, 514 at 6 inches, 255 at 12 inches and 155 at 18 inches. 955 to 514 is a factor of 1.86, and 514 to 255 is 2.02, but the last step is shallower: 255 to 155 is a factor of only 1.65.

The same shape shows up in other fixtures on that page. A TwinStar 900SA at 65 W reads 510, 360, 218 and 165 across the same four depths — a drop of only 24% over the last six inches. A Beamsworth DA 60 at 30 W goes 332, 179, 96, 64. A Nicrew ClassicLED G2 at 27 W, averaged from two users, falls off a cliff early (291 to 97 between 3 and 6 inches) and then flattens to 80 and 60. The Fluval 3.0 at 59 W gives 543, 288 and 136, with no 18-inch reading published.

No source in this set offers a rule for converting a published reading to another depth or position, or explains the shape of the falloff.

One caveat that matters more than the arithmetic. Those Chihiros figures were taken with a Samsung S22 Ultra running Photone. No source addresses whether phone-app readings are comparable to meter readings, or what the error is.

Same total light, different outcome: the DLI table

Daily light integral is one way to think about the disagreement over photoperiod, though no source gathered here mentions it. PAR is an instantaneous rate in µmol/m²/s; multiplied by the seconds of photoperiod it gives moles per square metre per day. The arithmetic: PAR × hours × 0.0036 = DLI.

Run it and the equivalences fall out. 20 PAR for 10 hours is 0.72 mol/m²/day. 40 PAR for 5 hours is 0.72 mol/m²/day. Same total photons at the leaf. A few more, since the conversion is worth having on paper:

• 20 PAR × 8 h = 0.58 mol/m²/day
• 30 PAR × 8 h = 0.86
• 50 PAR × 8 h = 1.44
• 50 PAR × 12 h = 2.16
• 80 PAR × 6 h = 1.73
• 100 PAR × 8 h = 2.88

Aqueon recommends 12 hours for planted tanks and Buce Plant about 8; at 30 PAR those work out to 1.30 and 0.86 mol/m²/day respectively. No source reconciles the two recommendations or addresses whether PAR and photoperiod trade off.

Whether the equivalence holds in practice is not something any source here addresses: none discusses photosynthetic saturation, carbon limitation, or how a short high-PAR burst compares with a longer dimmer one.

The algae question is directly contested and no source offers evidence either way. Aquarium Co-Op notes that slow-growing low-light plants collect algae on their leaves under constant bright light, Aqueon blames overly intense light in unplanted tanks, then concedes that nutrient build-up causes more outbreaks than lighting does. Sunken Treasure Aquatics goes further and argues more light makes a tank more algae-resilient, because algae is an imbalance. Neither claim is supported with a test, a mechanism, or a threshold.

Product	Material	Item Weight	Color	Included Components	Suits
VIPARSPECTRA 165W	—	7.6 pounds	Black	1 x Timer 165W, 1 x Wireless Remote, 1 x User Instruction, 1 x 6ft US Power Cord, 2 x Hanging Kits	Best for deep reef tanks
Lominie	Plastic	—	S20 Saltwater	Light kit inlcuded	Best for nano reefs
NEOAQLUX 24/7	Acrylonitrile Butadiene Styrene (ABS), Metal, Polyvinyl Chloride (PVC)	—	Black	Lamp Body ×1, Brackets ×2, Power Adapter ×1, User Manual ×1	Best for standard planted tanks
SEAOURA Clip	Aluminum	0.55 kg	White	Light kit inlcuded	Best for small clip-on setups
SEAOURA Led	—	1.1 pounds	Black	Bulb, Extendable Mount, Power Cable, User Manual	Best simple controls

Spec columns quote the listings verbatim. “Suits” is editorial.

Sort it in ten seconds

• VIPARSPECTRA 165W, not for you if this matters: 7.6 pounds and ceiling-mount only, so it needs a hanging kit or overhead support, not a tank rim.
• Lominie, not for you if this matters: only a single light source over a 2.7 in diameter head, so coverage is a pool rather than a bar.
• NEOAQLUX 24/7, not for you if this matters: no PAR or PPFD figure published, so depth suitability must be inferred.

Reef PAR and planted PAR are not the same claim

Nothing in the sources gathered gives reef PAR targets, coral placement heights, or a comparison of how reef and planted PAR figures are quoted. What the sources do say about reef lighting is narrower.

PAR by definition counts everything from 400 to 700 nm across the band, and no source addresses whether that flat treatment over-credits wavelengths the same sources call useless for growth. Aquascape Guide makes the point bluntly — reef lights output enormous PAR with a spectrum not optimised to grow plants. Buce Plant's rule of thumb for planted tanks runs the other way, red at 50% or more of the spectrum with blue capped near 15%.

Water absorbs red and yellow more readily than green and blue, so deep tanks need extra output at the warm end of the spectrum, and Aqueon states that blue wavelengths in particular penetrate deeper into water than others. No source works out what this means for spectrum choice at a specific depth, or whether a red-heavy spectrum survives 24 inches of water.

The five fixtures against those criteria

The evidence file contains no specifications for the VIPARSPECTRA, NEOAQLUX, SEAOURA or Lominie fixtures, so no claims about their PAR output, coverage, LED counts or ratings can be made here.

On the shading problem, Buce Plant's guide notes that a single wide-bar fixture can leave shaded areas despite a high PAR rating, and that distributing two or more sources improves coverage.

Fixing a light you already own, ranked by how much PAR it removes

The Chihiros figures show that 514 PAR at 6 inches falls to 255 at 12 — though those are depth readings in a tank, not a test of raising a fixture, and no source measures the effect of mounting height directly.

• Raise the fixture. Mounting height is one of the factors Sunken Treasure Aquatics names as determining how much light reaches the substrate, though no source quantifies the reduction.
• Dim, but check where the low end stops. Aquarium Co-Op's Easy Plant LED dims from 10-100%, which the maker presents as covering low, medium and high light plants.
• Shorten the photoperiod. It cuts the daily total, not the instantaneous intensity.
• Float plants for shade. Aquarium Co-Op lists floating and tall plants alongside lids, tannins and surface ripple as things that cut delivered PAR. Aquarium Co-Op does advise that low-light, slow-growing plants belong near the substrate or in shade.

On a fixture you cannot raise, dimming is your only intensity control.

VIPARSPECTRA 165W — Best for deep reef tanks

• Listed as balanced for PAR output over a 24 in x 24 in coverage area, the only pick specified in coverage terms
• 55 light sources across a 16 in wide fixture with a polished aluminium body for heat load
• But: 7.6 pounds and ceiling-mount only, so it needs a hanging kit or overhead support, not a tank rim
• But: Not waterproof, so it is unsuited to open-top splash or a humid hood

Lominie — Best for nano reefs

• Ships with both 60 degree and 180 degree optical lenses, so the beam can be narrowed to push intensity deeper or widened for spread
• 360 degree rustproof gooseneck clips on, useful for rimless tanks, sumps and refugiums
• But: Only a single light source over a 2.7 in diameter head, so coverage is a pool rather than a bar
• But: Listing quotes 110 lumens maximum output, low for the wattage figures given

NEOAQLUX 24/7 — Best for standard planted tanks

• 112 light sources, the densest LED count here, spread along a bar sized for 24-30 in tanks
• Extendable brackets sit on the rim, so no clip strength or hanging hardware is needed
• But: No PAR or PPFD figure published, so depth suitability must be inferred
• But: Brightness steps start at 20%, with no finer low end for shade plants or algae control

SEAOURA Clip — Best for small clip-on setups

• Adjustable height on the clip, the practical way to raise or lower PAR at the substrate without a dimmer
• 16 selectable time points and 5 timer settings, the finest scheduling control in this group
• But: Only 2 light sources at 12 W, so it will not drive demanding plants in anything deep
• But: Cycle mode locks out intensity adjustment, so you choose scheduling or dimming, not both

SEAOURA Led — Best simple controls

• Three physical push-button keys cover timer, brightness and colour, with no remote to lose or app to pair
• 10 brightness levels plus three colour modes, including a blue-only night setting
• But: Not waterproof, a real limitation on an open-top tank
• But: Timer offers only 6, 10 or 12 hour runs, and it counts from when you press it rather than a clock time

Back to the melting carpet: which of these suits which tank

Buce Plant's position is that a single wide-bar fixture can leave shaded areas despite a high PAR rating, and that distributing two or more sources improves coverage.

The evidence gathered here supports no fixture-by-fixture assignment: none of these products, their coverage areas, emitter counts, lenses or ratings appear in any source consulted.

Aquarium Co-Op's own conclusion is the one I'd keep: chasing specific PAR values matters less than knowing your plants' needs and watching their growth over time.

Which one, then?

VIPARSPECTRA 165W, best for it is the right answer for a deep reef tank where corals near the sand bed still need usable PAR, since it is engineered around PAR output across a 24x24 in footprint and hangs above the rim rather than clipping to it.

If your case is different:

• For it is the right answer for a nano tank or a refugium where the fixture must reach over an odd rim and the beam angle needs narrowing to concentrate PAR at depth: Lominie.
• For it is the right answer for a standard 24 to 30 inch freshwater planted tank where the light must sit on brackets across the rim and run a full day-night cycle unattended: NEOAQLUX 24/7.
• For it is the right answer for a small 7 to 12 inch tank or shrimp bowl where the light must clip to the side and its height above the water needs adjusting to tune intensity: SEAOURA Clip.

The VIPARSPECTRA 165W’s weak spot: 7.6 pounds and ceiling-mount only, so it needs a hanging kit or overhead support, not a tank rim