Incandescent lights work by heating a wire filament until it glows. They are the least-efficient of all the types of grow lights compared here, and are being phased out across the globe for this reason.
Intensity of Incandescent vs. LED Grow Lights
Incandescent lights are very dim compared to any other technology; watt-for-watt LEDs are more than 10 times as intense.
Spectrum of Incandescent vs. LED Grow Lights
Incandescent light bulbs produce mostly red light, then orange, yellow, green and blue in decreasing amounts. Their ratio of red to blue light is not ideal for growing plants, so many incandescent bulbs sold as grow lights have a blue filter applied to block much of the excess red light, making them even less efficient. LED grow lights can have a vastly superior plant-growing spectrum when properly designed.
Lifespan of Incandescent vs. LED Grow Lights
Incandescent bulbs fail when the filament inside breaks, and have very short lifespans. When used 12 hours or more per day for growing plants, the bulbs typically fail within 2 months. LED grow lights last 30-60 times longer!
Efficiency of Incandescent vs. LED Grow Lights
Incandescent lights are so inefficient that they are being phased out or banned by many countries for architectural use. The power required by incandescent lights to grow plants has always precluded them from being used in any serious indoor garden as a sole source of light. LEDs are more than 10 times as efficient at creating light, and with the right spectrum LED grow lights can easily be more than 20 times as efficient as incandescent lights.