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How much light do your plants need? LED guide by grow space

Light is the fuel for your plants. Without the right intensity, the proper spectrum, and uniform distribution, the rest of your setup—nutrients, substrate, climate—cannot perform at its full potential. By 2026, state-of-the-art LEDs have completely surpassed traditional HID systems (HPS, CMH) in efficiency, spectrum, and operating cost. This comprehensive guide explains everything you need to know to choose, install, and maximize your LED lighting system in Costa Rica.The Light Spectrum Your Plants NeedPlants don't see light the way we do. For them, certain wavelengths are fundamental for different biological processes: Blue (400-500 nm): Drives vegetative growth, compact leaf development, and chlorophyll formation. Plants under primarily blue light tend to be more compact with dark, healthy leaves. Essential during the vegetative stage. Green (500-600 nm): Penetrates deeper into the canopy than blue or red light. Contributes to photosynthesis in lower leaves that receive less direct light. LEDs that appear white primarily emit green/yellow light. Red (600-700 nm): Most efficient for photosynthesis. Drives growth, stretching, and especially flower formation and bulking. Essential during the flowering stage. Far-Red (700-750 nm): Does not directly contribute to photosynthesis but has important hormonal effects: stimulates the Emerson effect (increases red light efficiency), can accelerate flowering, and signals the presence of direct sunlight (important for the plant's circadian rhythm). UV (280-400 nm): In controlled doses, UV light slightly stresses plants and stimulates them to produce more trichomes as protection. Some premium LEDs include UV diodes for this reason. PPFD, DLI, and PPE: The Vocabulary of LightTo intelligently compare lights, you need to understand these three concepts:PPFD (Photosynthetic Photon Flux Density)Measures how many photosynthetically active photons reach a 1 square meter area per second. It is expressed in μmol/m2/s. It is the most important number for evaluating the intensity of a light on your plants.DLI (Daily Light Integral)The total photons a plant receives during an entire day of light. It is calculated as: DLI = PPFD x seconds of light per day / 1,000,000. The optimal DLI for most indoor crops is between 25-45 mol/m2/day.PPE (Photon Photosynthetic Efficacy)The efficiency of the light: how many micromoles of photons it produces per watt consumed (μmol/J). Modern high-quality LEDs achieve 2.5-3.0 μmol/J. Mid-to-low range LEDs are between 1.8-2.4 μmol/J. Old HPS rarely exceed 1.7 μmol/J.Target PPFD by Stage Stage Target PPFD (μmol/m2/s) Hours on Target DLI Germination / Seedling 200 - 400 18h 13 - 26 Vegetative 400 - 700 18h 26 - 45 Flowering 600 - 900 12h 26 - 39 Peak Flowering 800 - 1100 12h 35 - 47 Watts per Square Meter: The Practical GuideFor most growers without PPFD measuring equipment, the watts per m2 guide is the most practical way to size lighting: Crop Type Actual Watts per m2 Example for 1.2x1.2m (1.44 m2) Vegetative 250 - 350W/m2 360 - 504 Actual Watts Standard Flowering 350 - 500W/m2 504 - 720 Actual Watts High-Intensity Flowering 500 - 700W/m2 720 - 1000 Actual Watts Important: The actual watts consumed from the wall are what matters, not the nominal power that manufacturers often exaggerate.Light Distance GuideThe distance between the light and the canopy determines the intensity plants receive. Too close = light burn; too far = stretched plants reaching for light. As a general reference for quality LEDs: LED Power Distance in Vegetative Distance in Flowering 100-200W 40-60 cm 30-50 cm 200-400W 50-70 cm 40-60 cm 400-600W 60-80 cm 45-65 cm 600-1000W 70-90 cm 50-70 cm Always adjust according to plant response. If upper leaves look pale or have dry edges, move the light further away. If plants stretch too much, move it closer.LED vs HPS vs CMH: The Honest Comparison Characteristic Modern LED (2024+) HPS CMH (Light Emitting Ceramic) Efficiency (μmol/J) 2.5 - 3.1 1.5 - 1.9 1.9 - 2.1 Heat Generated Low Very high Moderate Room Heat Low (LED does not radiate infrared heat) High (30-40% of consumption goes to heat) Moderate Spectrum Full spectrum customizable Deficient in blue Very complete (best among HID) Lifespan 50,000 - 100,000 hours 10,000 - 20,000 hours 20,000 hours Initial Cost High Low Medium-high Operating Cost Low (less consumption per μmol) High Medium Harvest Quality Excellent (full spectrum) Good Excellent (similar to LED) How to Maximize Uniformity in Your Grow RoomA single light in the center of the room produces a high-intensity spot directly below and weaker areas at the edges. Perfect uniformity means all plants receive similar PPFD: Reflective walls: Mylar reflects up to 97% of light. White walls reflect 85-90%. Never use dark colored walls. A well-reflective room can increase effective PPFD by up to 20-30%. Multiple distributed lights: Two 300W lights evenly distributed cover a 1.2x2.4m space better than a single centered 600W light. Diffusers and lenses: Some LEDs come with secondary lenses that distribute light at a wide angle. Look for lights with a 120° or wider emission angle for better coverage. Plant rotation: In rooms where uniformity is not perfect, rotating plants 90° or 180° weekly compensates for intensity differences. Electricity Cost in Costa Rica: The Real CalculationICE (Instituto Costarricense de Electricidad) applies tiered rates. For normal residential use (T-RE rate), the approximate cost in 2026 is: First 200 kWh/month: ₡75-90 per kWh 200-500 kWh/month: ₡90-120 per kWh More than 500 kWh/month: ₡120-150 per kWh A 400W actual LED consuming 12 hours a day = 4.8 kWh/day = 144 kWh/month just for the light. Adding fans (100W x 18h = 54 kWh/month), extractor (60W x 18h = 32 kWh/month), and dehumidifier (400W x 8h = 96 kWh/month) brings the total to approximately 326 kWh/month for a 1.2x1.2m setup. At an average of ₡100/kWh, this is approximately ₡32,600/month in electricity.ROI: When Do I Recover My Investment in a Good LED?A quality LED (300-400W actual, 2.5+ μmol/J) costs more than a cheap one, but the difference is recovered through less electricity over time. Additionally, less heat means less work for the dehumidifier and extractor, which multiplies the savings.As a general rule: a quality LED pays for itself in 2-3 harvests compared to a low-quality LED that requires more watts for the same PPFD and yields inferior results.LED Brands Available in Costa RicaAt Costa Rica Hydroponics, we have LED lights available in various quality and price segments: Entry-level: 100-300W actual LEDs with Samsung or Epistar chips. Ideal for small rooms from 60x60 to 90x90 cm. Mid-to-high range: 300-600W actual LEDs with efficiency over 2.4 μmol/J, power dimmers, and uniform coverage. The optimal point between price and performance. Professional range: 600W+ LEDs with distributed bars, external controllers, and 2.7-3.0 μmol/J. For growers maximizing production per m2. Frequently Asked Questions Can I use outdoor LEDs (like floodlights or spotlights) for my plants? It is not recommended. Household or outdoor LEDs are not designed with the correct spectrum for photosynthesis and do not have the necessary intensity. They may work for decorative houseplants, but for serious cultivation, you need specific grow lights. Should I turn off the light completely during the 12 hours of darkness in flowering? Yes, completely. Even a very dim light during the dark period can interrupt the hormonal signal that drives flowering. Ensure no external light sources enter the room. Is it better to use 18/6 or 20/4 in vegetative? 18/6 is standard and works excellent. Some growers use 20/4 to accelerate growth, which can work, but the difference is not as significant as many believe. The most important thing is consistency—the same schedule every day. How much heat does an LED generate compared to an HPS? A 400W actual LED raises the room temperature by approximately 3-5°C. A 400W HPS raises it by 8-12°C because a large part of its energy is converted into radiant heat (infrared) instead of light. In CR, where heat is already a challenge, this difference is significant for climate management. What is the lifespan of a quality LED? Quality LEDs (Samsung LM301B/H, Osram, or similar chips) have a lifespan of 50,000-100,000 hours, with a luminous emission degradation of 70% (L70) at 50,000 hours. In practice, with 18 hours of daily use, that's 7-15 years before the light significantly loses efficiency. ConclusionLighting is the most impactful investment in any indoor setup. A good, state-of-the-art LED produces superior harvests, consumes less electricity, generates less heat (critical in CR's climate), and lasts for years. The difference between a quality LED and an economical one is not seen in the paper specifications—it is seen in the harvests, in the electricity bill, and in the climate management of your grow room.If you have questions about which light best suits your space and budget in Costa Rica, the Costa Rica Hydroponics team can recommend the right option. We bring the experience of having installed and tested dozens of systems in real tropical cultivation conditions.