More light doesn't mean a better aquarium. It often means more algae, stressed fish, and bleached corals. Getting lighting right is about matching the light to what you're keeping.
The lighting question stumps a lot of beginners because the options are overwhelming and the advice online tends to be written by people who've been in the hobby for years and are running high-tech setups. What works for a Dutch planted tank with CO2 injection is completely wrong for a simple community tank with a few low-tech plants.
What lighting actually does
For fish: lighting affects their day/night cycle and behavior. Most fish need a consistent photoperiod — 8 to 10 hours of light per day is standard. The intensity matters less for fish than for plants and corals, though many fish look better and show more natural behavior under lighting that mimics their natural environment.
For plants: lighting drives photosynthesis. More light means faster growth, but only if CO2 and nutrients can keep up. In a low-tech tank without CO2, more light just feeds algae. In a high-tech tank with CO2 injection, high light enables demanding plant species and dense growth.
For corals: different corals have dramatically different light requirements. Mushrooms and many LPS corals do fine under moderate light. SPS corals (acropora, montiporas) need intense, specific-spectrum lighting to grow and show their best colors. Getting this wrong is expensive — SPS frags aren't cheap.
Understanding PAR, PUR, and lumens
Lumens measure total light output as perceived by the human eye. They're useful for room lighting but nearly useless for aquariums because the human eye is most sensitive to green and yellow light, which plants and corals use less efficiently.
PAR (Photosynthetically Active Radiation) measures light in the wavelengths that plants and corals actually use — 400 to 700 nanometers. This is the number that matters. PAR meters are expensive ($200+) but reef hobbyists typically consider one essential.
PUR (Photosynthetically Usable Radiation) is a step further — it accounts for the fact that plants use some wavelengths more efficiently than others. Full-spectrum LEDs score better here than narrow-spectrum fixtures.
LED vs T5 vs metal halide
LED is the dominant technology now for good reason. Energy efficient, low heat output, long lifespan, and modern LEDs can be tuned for specific spectrums. The quality range is enormous — a $30 LED from Amazon is not the same as a $400 Radion. For freshwater, most quality LED fixtures work well. For reef, the spectrum and intensity matter a lot more and budget matters less.
T5 fluorescent is still used in serious reef and planted tank setups because the coverage is even and predictable. T5 fixtures don't have the hot spots and shadowing that single-point LEDs can create. Some experienced reefers run T5/LED hybrid setups. For most beginners this is more complexity than you need.
Metal halide was the reef standard before LEDs and is still used in some large systems. Excellent PAR output and spectrum, terrible heat generation and energy efficiency. Hard to justify for new setups.
Photoperiod and algae
Algae is the most common symptom of too much light. If you're fighting persistent algae — green spot algae, green hair algae, cyanobacteria — the first thing to try is reducing your photoperiod. Drop from 10 hours to 8 hours and see if it improves over two weeks.
Running lights on a timer is non-negotiable. Inconsistent photoperiods stress fish and make algae problems worse. Set it and forget it — the same hours every day.