How Much Light Do Microgreens Need?

Light is the most frequently misunderstood resource in microgreens growing. Many beginners assume a windowsill is always sufficient — and in ideal conditions it can be — but inadequate light produces tall, pale, spindly shoots with poor flavour and a significantly reduced nutritional profile. Understanding what microgreens actually need from light, and how to provide it reliably throughout the year, makes the difference between a mediocre harvest and a genuinely excellent one.

Light Intensity and Duration

Microgreens need at least 10 to 12 hours of light per day during the growing phase. They are most productive — greener, more compact and flavourful — at 14 to 16 hours per day. This is because microgreens are in a juvenile growth stage and have a high photosynthetic demand relative to their size; they are building energy reserves at a rate proportional to their leaf area, and more hours of light means more energy available per day.

Light intensity matters as much as duration. Low-intensity light (a north-facing window in winter, for example) can trigger the same elongation response as no light at all — the plants stretch in search of stronger light. Aim for bright, direct or near-direct light from a south-facing window in summer, or supplement with artificial light year-round.

Grow Light Options

T5 fluorescent shop lights are the budget-friendly standard for home microgreens growing. A standard two-tube 60 cm fixture provides adequate light for a 10×20-inch tray when positioned 5 to 10 cm above the canopy. These lights are inexpensive, widely available and produce very little heat. The main limitation is energy consumption compared to LEDs.

Full-spectrum LED grow panels are more energy-efficient, last longer and often provide a broader spectrum that includes red and blue wavelengths particularly useful for plant growth. They cost more upfront but pay back over time in electricity savings. For a home grower running one or two trays, a basic LED grow strip or panel costing £15 to £30 is adequate. Look for a colour temperature of 5000 to 6500 K (daylight spectrum) or a purpose-made "full spectrum" grow light.

Signs of Insufficient Light

Leggy, pale-green or yellow shoots that stretch toward the light source are the clearest sign of light deficiency. The stems will be long and thin relative to the leaf size, and the shoots may be floppy rather than upright. Flavour is noticeably milder or even bland in light-starved microgreens. If you see these signs, move the light closer to the canopy (stop when you can feel warmth on your hand at canopy level — that is too close), extend the photoperiod, or move the tray to a brighter location.

Light During the Blackout Phase

During the first 3 to 4 days of germination, microgreens are kept in darkness under a covered tray. This is intentional: darkness encourages the seedling to push upward through the medium quickly, and the absence of light during germination actually promotes stronger initial stem development. The covered blackout phase is NOT a problem — it is a feature. Light is only needed once the tray is uncovered and the seedlings are moved to their growing position.