Heat Production

• Both CFL and LED grow lights utilize electricity efficiently in the creation of visible light. LEDs emit a small amount of heat when lit; grow lights are available that feature clusters of many LEDs in one bulb. A group of LEDs can offer a considerable light output. CFL grow lights waste little in heat production while emitting light but they are still not as efficient as LEDs. However, you can place them in relatively close proximity to each other without posing an increased fire risk.
  
  

Output

• Light output differs between CFL and LED grow lights. One LED cannot produce the same output as even a low-wattage CFL. Light output is measured in lumens. The average LED grow light offers approximately 20 lumens per watt output. One 42-watt CFL grow light offers approximately 65 lumens per watt output.
  
  

Quality

• Plants utilize certain qualities of light to grow at different stages of development. Quality refers to the color of visible light. Blue light, with wavelengths between approximately 400 and 480 nanometers in the visible light spectrum, promotes leafy growth in plants. Red visible light, with wavelengths between 600 and 680 nanometers, promotes the flowering process. LEDs can emit light in different wavelengths. Blue and red LEDs are ideal for promoting growth in all major phases of a plant's development. CFLs emit white or whitish-blue light. This type of light is ideal for vegetative growth and to promote growth in seedlings.
  
  

Mercury

• Another advantage that LEDs offer as compared to CFLs is that they do not require elemental mercury to produce visible light. The average CFL contains approximately 4 to 5 mg mercury, which can be harmful if ingested. The Environmental Protection Agency claims that mercury exposure can lead to harmful side effects. Exposure to high levels of mercury can even be fatal.
  
  

Lifespan

• One of the largest differences separating CFLs and LEDs is lifespan. LEDs are designed to last longer than CFLs. The average LED can operate for more than 50,000 hours. CFL grow lights are only designed to last for up to 10,000 hours.