Human and Plant Lighting requirements are, for the most part, distinctly different wavelengths within the spectrum. We measure these wavelengths in nanometers. Studies have proven that plants receive some benefit with a small amount of light from the human wave spectrums but the vast majority of their needs come in the form of Ultraviolet (380 nanometers) and Infrared (720 nanometers) wavelengths of the spectrum.
Ultraviolet to Infrared Wavelength Spectrum
When selecting any lamp it's important to have a basic understanding of how both the quality and quantities of the selection not only enhances the ability for us to see, but how much energy does it take to accomplish this task. In the charts below you will see comparisions of different lamps and their comparitive efficiencies.
For plant lighting, higher lamp efficiencies, within the proper spectrums, means less operating costs by lowered wattages, lower heat generation by the lamp/ballast, maximum canopy penetration, long lamp life and minimum lumen depreciation will all contribute to succesful grows.
How People See Light
For human vison we design lighting levels with two distinct kinds of lumen output. The first is called Photopic or Design Lumens, which represents the relative sensitivity of the eye under intense lighting such as daytime cloudless outdoor sun conditions. Photopic lumen output is registered by the cones in the human eye and is measured in Lumen, Lux and Foot Candles.
The second type of lumens are called Scotopic, which represent the sensitivity of the eye under typical interior or night lighting conditions and cannot be measured directly with a standard light meter. Scotopic lumen output is registered by the rods of the human eye and also controls pupil size directly effecting visual acuity for given task levels.
Measuring Light, Energy and Efficiencies
Below we show how different light sources Design Lumen readings compare when read by a standard light meter and measured in Conventional Photopic Lumen values. For lighting design that wishes to maximize energy efficiencies by specifying light sources with both high Scotopic and Photopic Lumens, a Correction Factor (S&P Ratio) must be applied to the Photopic Lumen per Watt readings.
When applying this correction factor you will notice drastically different usable light outputs as measured in Pupil Lumens per Watt. Higher Pupil Lumens per Watt will significantly reduce the amount of energy necessary to satisfy maximum visual acuity within the optimal yellow-green regions of the spectrum. In other words; the higher the Pupil Lumens/Watt the less energy will be required of the lamp for the eye to accurately see what it's
To illustrate this you can see by the charts below that the LPS (Ugly Yellow Street Lighting) lamp is more efficient from a conventional efficacy (Lm/W) perspective. However the LPS has a very low S/P ratio and poor pupil lumens per watt when compared to induction. Now the CRI and the VEL would indicate poor visual acuity. What this means is that while there may be a high lumen per watt when using LPS, the ability to accurately gauge the color of what we are observing is extremely poor.
Measuring Energy Efficiency Design Lumens
Conventional Lumens per Watt
Correction Factor (S&P Ratio)
Pupil Lumens per Watt
Induction Lamp (5000K)
Warm White Fluorescent (2900K)
High Pressure Sodium (50W)
Delux Mercury Vapor
Induction Lamps: Why They Appear Brighter
Below we show how Photopic and Scotopic Values vary between different lamp types and how bright they will then appear to the eye. This is known as Apparent Brightness and is not measured in the conventional Lumens, Lux or Footcandle readings.
There are a number of terms engineers use that reference Apparent Brightness; Visually Effective Lumens (VEL), Spectrally Effective Lumens (SEL) or Pupil Lumens as this measurement, but whatever phrase you use, they all refer to the same thing: Apparent Brightness.
High Pressure Sodium
Metal Halide (Pulse Start)
Standard Units of Measurement for Vision
When taking into account the standard photometric measurements of light for human vision the system of units we measure would be the LUMENS which measures the total amount of light emitted from a source.
This light is then distributed over an area and the illuminated area is measured in LUX. LUX is measurement of intensity as percieved by the human eye. It is a way of measuring how many LUMENS fall within a square meter of an illuminated surface.
The difference between the LUX and the LUMEN is that a LUX measures the area over which the LUMEN is distributed. These levels are inversely proportional to the area being lit. The larger the area the lower the intesity of the LUX levels. For example a reading of 1000 LUMENS would correlate to 1000 LUX at a 1 meter area however the LUX illumination levels would fall to 100 LUX over a 10 meter area.
In the United States you'll often hear light measurements in FOOTCANDLES. This term is used alot in construction related projects and by engineers who deal with US Standards of measurement. LUX and FOOTCANDLES are different units of the same quantity in that FOOTCANDLE will measure the amount of LUMEN PER SQUARE FOOT whereas LUX measures the LUMENS PER SQUARE METER. Other then in the United States you will not usually hear light measured in FOOT CANDLES.
Since all light is emitted in wavelengths, and we know that the human eye can see certain wavelengths better then others, with the peak being measured @ 555 nanometers, we can now determine a given lamps source LUMENS PER WATT.
The LPW measurement adjusts for the spectral wavelengths the lamp produces. So when determining a task level of illumination for human eyesight, we can decide which lamp will best suit the task for the least amount of wattage, with factored depreciation, and how important the color, as measured in the CRI, to best match the task.
Measuring Induction Lighting Efficiencies
Induction lighting systems surpass traditional HID lighting systems in the combined CRI and the Scotopic/Photopic (S/P) Ratios.
Of the wide variety of energy efficient lamp choices on the market today Inda-Gro Induction Grow Lighting more closely represents natural sunlight and provides the highest VEL Lm/w while still peaking in the 380 and 720 nanometer ranges.
Additionally our grow lights, with ballast efficiencies of 95%, have demonstrated to best imitate the advantages of the higher wattage HID lamps while saving up to 70% less wattage per fixture.