光谱是指植物生长灯发出的波长分布。PAR 范围（400–700 纳米）内的不同波长对植物生长有不同的影响：蓝色波长（400–500 纳米）促进紧凑的营养生长，红色波长（600–700 纳米）驱动光合作用和开花，远红色波长（700–800 纳米）影响茎伸长和避荫反应。全光谱 LED 试图通过组合多个波长来近似模拟自然阳光。
关键事实
- Blue (400–500 nm): compact growth, thick leaves, strong root development
- Red (600–700 nm): peak photosynthetic efficiency, flowering trigger (short-day plants)
- Far-red (700–800 nm): stretching, canopy penetration, Emerson enhancement effect
- Green (500–600 nm): partially used by plants; penetrates deeper than red/blue
- Full-spectrum LEDs mimic natural sunlight; white LEDs use phosphor conversion
- Red:Blue ratio affects plant morphology — higher blue = more compact plants