naoki
Well-Known Member
Bjorn, if you switch on and off HPS, doesn't it influence the life of bulbs and ballasts quite a bit?
Bjorn and Rob, I quote this paper frequently, but here is actual comparison of efficiency (table 3).
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0099010
As Bjorn said, the efficiency of the top HPS is similar to the top LED. But majority of LEDs have lower efficiency than HPS. If you do DIY LED, you can squeeze out the efficiency.
I've also wondered about the heat issue. I've never used HPS, but it seems to be hot compared to the LED with the same input watt. The input energy goes either to light or heat, so if the efficiency is similar, they should release the same amount of heat. But one thing that I may be missing in this way of thinking is that photons with different wavelengths have different energy levels. The efficiency of both best HPS and LED is around 1.7 micromol/s/W (=micromol/J). However, the emission spectra is different, actual energy used to produce the same 1.7 micromol of photons is different. For example, using an extreme case, let's say LED uses all Blue. HPS emission peak is around yellow. 1 blue photon requires more energy production than yellow photon. So even if they both get the same photon efficiency, LED is converting more energy to light and less energy to heat than HPS. But in reality, those top level LEDs use lots of red, which has lower energy than yellow. So it is still puzzling why LED seems to be cooler.
To compare the heat emission of LED vs HID, we need the efficiency in terms of emitted light watt per given input watt (instead of photon efficency or lumen efficacy).
Bjorn and Rob, I quote this paper frequently, but here is actual comparison of efficiency (table 3).
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0099010
As Bjorn said, the efficiency of the top HPS is similar to the top LED. But majority of LEDs have lower efficiency than HPS. If you do DIY LED, you can squeeze out the efficiency.
I've also wondered about the heat issue. I've never used HPS, but it seems to be hot compared to the LED with the same input watt. The input energy goes either to light or heat, so if the efficiency is similar, they should release the same amount of heat. But one thing that I may be missing in this way of thinking is that photons with different wavelengths have different energy levels. The efficiency of both best HPS and LED is around 1.7 micromol/s/W (=micromol/J). However, the emission spectra is different, actual energy used to produce the same 1.7 micromol of photons is different. For example, using an extreme case, let's say LED uses all Blue. HPS emission peak is around yellow. 1 blue photon requires more energy production than yellow photon. So even if they both get the same photon efficiency, LED is converting more energy to light and less energy to heat than HPS. But in reality, those top level LEDs use lots of red, which has lower energy than yellow. So it is still puzzling why LED seems to be cooler.
To compare the heat emission of LED vs HID, we need the efficiency in terms of emitted light watt per given input watt (instead of photon efficency or lumen efficacy).
