Best LED Lights for SPS and LPS Coral: PAR, Spectrum & Photoperiod Guide

SPS (small polyp stony) corals require 200–400 PAR (photosynthetically active radiation) at the coral surface, while LPS (large polyp stony) corals grow optimally at 50–150 PAR. Choosing the wrong light intensity is the most common reason coral bleach or fail to grow in home reef aquariums — and the most expensive mistake to diagnose after the fact.

Understanding PAR, PUR, and Spectrum

PAR measures the quantity of light photons in the 400–700nm range. PUR (photosynthetically usable radiation) measures the subset of PAR wavelengths actually absorbed by zooxanthellae (the symbiotic algae in coral tissue). Blue wavelengths (430–470nm) and red wavelengths (620–680nm) are highest in PUR for coral photosynthesis. A light with high PAR but a spectrum dominated by green (500–560nm) — the least useful wavelength for coral — will underperform a lower-PAR fixture with a reef-optimized spectrum.

PAR Requirements by Coral Type

Coral Type	PAR Range	Examples	Placement
SPS (high light)	250–400+ PAR	Acropora, Montipora	Top 1/3 of tank
SPS (medium light)	150–250 PAR	Stylophora, Pocillopora	Middle zone
LPS	50–150 PAR	Hammer, Torch, Frogspawn	Middle-bottom
Soft corals	30–100 PAR	Zoanthids, Mushrooms	Any zone
Mixed reef	100–200 PAR (average)	Varied	Aquascape dependent

LED Sizing by Tank Footprint

As a general rule, plan for 1–2 watts of quality reef LED per gallon for mixed reefs, and 2–3 watts per gallon for SPS-dominant systems. For tanks with a 24" x 24" footprint, a single 100–150W full-spectrum reef LED is typically sufficient. The Seatorch LM Series reef LED lights provide a full spectrum across UV, violet, blue, cyan, green, red, and white channels, with smartphone app control for custom spectrum tuning and sunrise/sunset simulation.

Setting a Reef Photoperiod

Most reef corals adapt well to a 10–12 hour photoperiod. Program your light controller to ramp up over 60–90 minutes at the start and ramp down at the end, simulating natural sunrise and sunset. This gradual transition reduces coral stress and prevents the "lights-on aggression" response seen in some LPS species. During peak hours (typically 3–4 hours midday), run the fixture at full intensity for the coral types you're keeping.

Acclimating Coral to New Lights

New corals should be introduced at 30–40% of target PAR and gradually increased by 10% per week. Bleaching occurs when zooxanthellae are expelled under sudden light stress — a process that can kill coral within weeks. Using a PAR meter during acclimation removes guesswork and prevents losses from improper light placement.

FAQ

How far should my LED light be from the water surface?

Most reef LED fixtures are designed to be mounted 6–12 inches above the water surface. Closer placement increases PAR but narrows the coverage footprint. Manufacturer specs typically provide PAR maps at standard mounting heights.

Do I need a PAR meter for my reef tank?

A PAR meter is the most reliable way to verify your coral is receiving appropriate light. Apogee MQ-510 is the standard reef-grade PAR meter. Many local reef clubs and fish stores offer PAR meter rentals.

How long should reef lights be on per day?

10–12 hours is standard for most reef systems. Avoid exceeding 12 hours, as extended photoperiods can encourage nuisance algae growth without additional benefit to coral.

Can I use freshwater planted tank LEDs for reef corals?

Not recommended. Planted tank LEDs emphasize green and red channels for plant photosynthesis, lacking the blue/violet channels critical for coral PUR and fluorescent protein expression.

Why are my corals not opening under my new LED?

Common causes: too much light (bleaching stress), too little flow (detritus on polyps), acclimation period (allow 1–2 weeks after tank introduction), or water chemistry issues. Check PAR, flow, and parameters before adjusting the light.