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Most efficient to produce not most efficient for plant growth. Context: "The company has developed a wavelength conversion system that uses phosphorous to conv

Most efficient to produce not most efficient for plant growth. Context: "The company has developed a wavelength conversion system that uses phosphorous to convert blue photons, which are the most efficient type of photon, into any other color photon."

logfromblammo 11y ago
If you're using phosphors, you do want to make blue or UV. It's far easier to step a photon down in energy than to absorb multiple lower energy photons and emit one at higher energy. But the highest efficiency color for LEDs to produce largely depends on what Cree and Nichia are doing this year. Unfortunately, most of the readily available numbers tout luminous efficiency rather than raw light power. That's fine if you're looking for a reading light, but chlorophyll does not have the same absorption spectrum as the opsins in the human eye. You have to look for "wall-plug efficiency", which is less commonly reported. So with respect to photons emitted per watt, I'm not sure which LED chemistry takes the prize. It depends on the temperature and input power, too. You can achieve 200% wall-plug efficiency, but only if you're converting picowatts of electricity into picowatts of photons in a hot LED. This is not possible (economically) for grow lights. The benchmark for grow lights is the low-pressure sodium lamp, at about 38% efficiency. LEDs maybe get 30-65%, considering transformers, internal resistance, quantum efficiency, reflective losses at the die-capsule interface, etc. Higher efficiency comes from more expensive components. As for chemistry, InGaN efficiency drops at longer wavelengths, and AlInGaP efficiency drops at shorter wavelengths, leaving a big efficiency trough in the green range. (Fortunately for this, plants don't need green.) I suspect that AlInGaP LEDs in the orange range are more efficient than visible blue InGaN LEDs, but this is hard to show with a lazy web search. So when you say "most efficient" you really have to be very explicit about the application. That was my implied complaint about that sentence in the article.

logfromblammo 11y ago

If you're using phosphors, you do want to make blue or UV. It's far easier to step a photon down in energy than to absorb multiple lower energy photons and emit one at higher energy. But the highest efficiency color for LEDs to produce largely depends on what Cree and Nichia are doing this year. Unfortunately, most of the readily available numbers tout luminous efficiency rather than raw light power. That's fine if you're looking for a reading light, but chlorophyll does not have the same absorption spectrum as the opsins in the human eye. You have to look for "wall-plug efficiency", which is less commonly reported. So with respect to photons emitted per watt, I'm not sure which LED chemistry takes the prize. It depends on the temperature and input power, too. You can achieve 200% wall-plug efficiency, but only if you're converting picowatts of electricity into picowatts of photons in a hot LED. This is not possible (economically) for grow lights. The benchmark for grow lights is the low-pressure sodium lamp, at about 38% efficiency. LEDs maybe get 30-65%, considering transformers, internal resistance, quantum efficiency, reflective losses at the die-capsule interface, etc. Higher efficiency comes from more expensive components. As for chemistry, InGaN efficiency drops at longer wavelengths, and AlInGaP efficiency drops at shorter wavelengths, leaving a big efficiency trough in the green range. (Fortunately for this, plants don't need green.) I suspect that AlInGaP LEDs in the orange range are more efficient than visible blue InGaN LEDs, but this is hard to show with a lazy web search. So when you say "most efficient" you really have to be very explicit about the application. That was my implied complaint about that sentence in the article.