PAR and Spectrum: Lighting for SPS Success

Lighting SPS: Beyond "Turn It Up"

Lighting is probably the single most impactful variable in SPS keeping after water chemistry. Getting it right means understanding what corals actually need from a light source.

PAR: What to Aim For

PAR (Photosynthetically Active Radiation) measures usable light reaching the coral. Target ranges at the coral surface:

Montipora: 150–300 PAR
Stylophora: 150–350 PAR
Acropora: 200–450 PAR
Seriatopora (birdsnest): 100–250 PAR

PAR drops significantly with depth — a fixture pumping 600 PAR at the surface might deliver only 200 at the sand bed.

Spectrum: Not Just Blues

Blue light (420–480nm) is essential, but running pure blue is a common mistake. A good SPS spectrum includes:

Royal blue (450nm): The workhorse wavelength for photosynthesis
Blue (470nm): Complements royal blue, drives fluorescence
UV/violet (390–420nm): Enhances fluorescent colours — but too much can bleach corals
Cool white: Fills in the spectrum and makes colours look natural to human eyes

Most modern LEDs (Radion, AI Hydra, Kessil) have presets that work well out of the box. Starting with the manufacturer's reef preset and tweaking from there is a sound approach.

Acclimating New Corals

Placing a new frag straight into high-PAR areas is a common cause of bleaching. The safer approach:

Place new frags in the bottom third of the tank
Leave for 2 weeks minimum
Move to the mid-section for another 2 weeks
Final placement in the upper third if desired

Photoperiod

Most SPS tanks do well with 8–10 hours of main lighting, plus 1–2 hour ramp up/down periods. Corals need a dark period for metabolic processes.

Budget Considerations for UK Reefers

Budget: Nicrew or basic LEDs, £80–150. Suitable for montis and stylos
Mid-range: AI Prime, Kessil A160/A360, £200–350. Will grow anything
High-end: Radion XR15/XR30, AI Hydra, £400–700+. Maximum control

Whatever the fixture, adjustable spectrum and intensity are essential for SPS.