Blake Boghorn
420 Member
Lighting info made my head spin the first time I did research. Here is the stuff I wish I knew before I purchased my light.
Don't use Watts, Lumens, or Lux as measurements for plant lights.
Watts is a measure of electricity and Lumens and LUX are measures of light as perceived by the human eye. You can use these measurements as proxies for light measurement after you know everything else. The measurements of light you should be using are PAR, PPF, PPFD and DLI.
PAR
PAR (photosynthetic active radiation) are the wavelengths of light found between 400 (blue) to 700nm (red). Coincidentally, this is also the visible spectrum which is why, at first, it's confusing you can't use Lumens or LUX to measure light for plants. There is no measure of PAR, so you can't say, for example, the PAR of this light is 800. PAR only represents light between 400 to 700nm and is used for to measure PPF, PPFD and DLI.
PPF
PPF (photosynthetic photon flux) is a measure of light emitted in the PAR range. This is measured in μmol/s. A μmol (micromole) is basically a hell of a lot of photons (6 x 101^7). Since we want to measure the rate of photons emmited, PPF is measured per second. Think of this as photons per second. PPF is measured at the source. This is less useful than PPFD because you are not measuring how much is available to a plant.
PPFD
PPFD (photosynthetic photon flux density) is very similar to PPF, only PPFD is measuring photons that reach a surface (m^2), so it's measured in μmol/s/m^2. This matters because a light that emits X PPF, will always emit X PPF, but will have different PPFD readings based on where you measure it. For example, you'll get the highest PPFD reading directly under a lamp and it will gradually decrease as you move further away. For seedlings and clones, a PPFD of 200-400 is sufficient, in veg (400-600), in flower 600-900. You can go even higher, especially if you add C02 to your environment. Random fact, on a bright, sunny day in the summer, the PPFD of the sun is 2000.
DLI
DLI (daily light integral) measures the photons that reach a surface (m^2) in a 24 hour period. It's measured in mol/m^2/day. To calculate DLI, you sum PPFD readings over 24 hours. A DLI of 22 is the bottom threshold and 65 is the top. DLI gets interesting when you start to think about light schedules. You can get the same DLI by using a lower intensity light, over a longer period. For example, If you don't have a light that puts out sufficient PPFD for an 18 hour light period, increase to 22 to hit your DLI. Same goes for flowering. Since you only have 12 hours to deliver light, crank it up to hit your DLI goal. There is research that shows plants are more efficient at photosynthesis (converting photons to energy) in lower light levels. Therefore, you can buy a smaller light for veg and use a longer schedule.
Watt Equivalent Claims are Garbage
Whenever you see something like 2000W Equivalent, take it with a grain of salt. The manufactures are claiming that the LED light is equivalent to a 2000W HPS, which is never the case. The only way to compare apples to apples is by getting a PPF measure. I would also stray away from using actual draw to compare LEDs to LEDs. For example, one LED may have an actual draw of 400W and another 200W, and you might be tempted to say the 400W light is twice as strong. You can measure efficiency by looking at μmol/joule, which tells you how efficient a light is at converting electricity (joules) to photons (μmols), it's called PPF Efficacy. Good manufactures advertise this. Good LED lights, for example, HLGs, can hit a PPF Efficacy of almost 3 and bad ones are in the low 1s. This means good LED are almost 3 more efficient at converting electricity to photos. You'd be consuming 3 times the electricity to get the same PPFD using the example above. The theoretical maximum is around 5 μmol/joule which means LEDs will only get more efficient in the coming years.
Light Spectrum
I mentioned earlier that PAR range is the same as the visible spectrum (400-700nm). This is true, however, plants and humans are sensitive to different wavelengths, so we use different measures of light intensity. Humans are more sensitive to green versus red and blue, and plants are more sensitive to red and blue versus green. For example, if you have one green LED diode and one red LED diode with the same wattage (don't mess with me), Lux will be higher on the green light versus the red light and vice versa. This is why you can't accurately use Lux to measure light used for plants, however, there is a caveat. If you know the spectrum, and I'm talking the exact spectrum, you can use a conversion factor to go from LUX to PPFD. For example, if you get the LUX of the sun and multiply it by 0.0185, that's a semi-accurate PPFD reading. Apogee Instruments has some conversion factors for common lights on their website. Google "LUX to PPFD apogee". You can DL a LUX meter on your phone, get a LUX reading, check if your light has a conversion factor, and use that to get a PPFD reading. You can't accurately use this method for LEDs because their spectrum is unknown (especially blurples). You can buy a PPFD sensor for around $300 and never have to worry again.
The theory behind blurple lights, is that if you can save on electricity by cutting down on green light (which plants don't use as much) and crank up the red and blue to optimal levels. This is possible with LEDs because of the individual diodes. For some reason, that theory hasn't panned out, although it does make sense logically. In almost all cases, white LEDs out perform blurple lights. It makes sense when you consider the sun is white light. There is research that plants use more infrared and UV light than we think, so the spectrums will continue to evolve.
Summary
I realize there isn't much practical advice in here, so I'll try to distill this down into a few sentences. Use accurate measures of light - stay away from watts, lux and lumens. You can use a free app to get a LUX reading and convert that to PPFD if your spectrum is known. Determine the light intensity you'll need for your grow space and purchase a light, from a reputable manufacturer knowing your requirements. Take into consideration the light's PPF, PPFD (at different distances), actual wattage draw and PPF efficacy. Look at HLGs (more expensive) or Spider Farmer (less expensive) for good, white LED quantum boards. I've also heard good things about Mars Hydro.
Don't use Watts, Lumens, or Lux as measurements for plant lights.
Watts is a measure of electricity and Lumens and LUX are measures of light as perceived by the human eye. You can use these measurements as proxies for light measurement after you know everything else. The measurements of light you should be using are PAR, PPF, PPFD and DLI.
PAR
PAR (photosynthetic active radiation) are the wavelengths of light found between 400 (blue) to 700nm (red). Coincidentally, this is also the visible spectrum which is why, at first, it's confusing you can't use Lumens or LUX to measure light for plants. There is no measure of PAR, so you can't say, for example, the PAR of this light is 800. PAR only represents light between 400 to 700nm and is used for to measure PPF, PPFD and DLI.
PPF
PPF (photosynthetic photon flux) is a measure of light emitted in the PAR range. This is measured in μmol/s. A μmol (micromole) is basically a hell of a lot of photons (6 x 101^7). Since we want to measure the rate of photons emmited, PPF is measured per second. Think of this as photons per second. PPF is measured at the source. This is less useful than PPFD because you are not measuring how much is available to a plant.
PPFD
PPFD (photosynthetic photon flux density) is very similar to PPF, only PPFD is measuring photons that reach a surface (m^2), so it's measured in μmol/s/m^2. This matters because a light that emits X PPF, will always emit X PPF, but will have different PPFD readings based on where you measure it. For example, you'll get the highest PPFD reading directly under a lamp and it will gradually decrease as you move further away. For seedlings and clones, a PPFD of 200-400 is sufficient, in veg (400-600), in flower 600-900. You can go even higher, especially if you add C02 to your environment. Random fact, on a bright, sunny day in the summer, the PPFD of the sun is 2000.
DLI
DLI (daily light integral) measures the photons that reach a surface (m^2) in a 24 hour period. It's measured in mol/m^2/day. To calculate DLI, you sum PPFD readings over 24 hours. A DLI of 22 is the bottom threshold and 65 is the top. DLI gets interesting when you start to think about light schedules. You can get the same DLI by using a lower intensity light, over a longer period. For example, If you don't have a light that puts out sufficient PPFD for an 18 hour light period, increase to 22 to hit your DLI. Same goes for flowering. Since you only have 12 hours to deliver light, crank it up to hit your DLI goal. There is research that shows plants are more efficient at photosynthesis (converting photons to energy) in lower light levels. Therefore, you can buy a smaller light for veg and use a longer schedule.
Watt Equivalent Claims are Garbage
Whenever you see something like 2000W Equivalent, take it with a grain of salt. The manufactures are claiming that the LED light is equivalent to a 2000W HPS, which is never the case. The only way to compare apples to apples is by getting a PPF measure. I would also stray away from using actual draw to compare LEDs to LEDs. For example, one LED may have an actual draw of 400W and another 200W, and you might be tempted to say the 400W light is twice as strong. You can measure efficiency by looking at μmol/joule, which tells you how efficient a light is at converting electricity (joules) to photons (μmols), it's called PPF Efficacy. Good manufactures advertise this. Good LED lights, for example, HLGs, can hit a PPF Efficacy of almost 3 and bad ones are in the low 1s. This means good LED are almost 3 more efficient at converting electricity to photos. You'd be consuming 3 times the electricity to get the same PPFD using the example above. The theoretical maximum is around 5 μmol/joule which means LEDs will only get more efficient in the coming years.
Light Spectrum
I mentioned earlier that PAR range is the same as the visible spectrum (400-700nm). This is true, however, plants and humans are sensitive to different wavelengths, so we use different measures of light intensity. Humans are more sensitive to green versus red and blue, and plants are more sensitive to red and blue versus green. For example, if you have one green LED diode and one red LED diode with the same wattage (don't mess with me), Lux will be higher on the green light versus the red light and vice versa. This is why you can't accurately use Lux to measure light used for plants, however, there is a caveat. If you know the spectrum, and I'm talking the exact spectrum, you can use a conversion factor to go from LUX to PPFD. For example, if you get the LUX of the sun and multiply it by 0.0185, that's a semi-accurate PPFD reading. Apogee Instruments has some conversion factors for common lights on their website. Google "LUX to PPFD apogee". You can DL a LUX meter on your phone, get a LUX reading, check if your light has a conversion factor, and use that to get a PPFD reading. You can't accurately use this method for LEDs because their spectrum is unknown (especially blurples). You can buy a PPFD sensor for around $300 and never have to worry again.
The theory behind blurple lights, is that if you can save on electricity by cutting down on green light (which plants don't use as much) and crank up the red and blue to optimal levels. This is possible with LEDs because of the individual diodes. For some reason, that theory hasn't panned out, although it does make sense logically. In almost all cases, white LEDs out perform blurple lights. It makes sense when you consider the sun is white light. There is research that plants use more infrared and UV light than we think, so the spectrums will continue to evolve.
Summary
I realize there isn't much practical advice in here, so I'll try to distill this down into a few sentences. Use accurate measures of light - stay away from watts, lux and lumens. You can use a free app to get a LUX reading and convert that to PPFD if your spectrum is known. Determine the light intensity you'll need for your grow space and purchase a light, from a reputable manufacturer knowing your requirements. Take into consideration the light's PPF, PPFD (at different distances), actual wattage draw and PPF efficacy. Look at HLGs (more expensive) or Spider Farmer (less expensive) for good, white LED quantum boards. I've also heard good things about Mars Hydro.
