By Richard Krueger
If you’re in the market for Grow Lights and have been doing your research, reviewing datasheets can often be a complicated and dizzying endeavor. The absence of standards means a wide variety of metrics can be included, and it’s anyone’s guess as to which ones are useful or not – until now.
Following are key metrics defined and what to look for in helping you with your LED purchasing decisions:
Light Spectrum
Photosynthetic Photon Flux (PPF) is a way to measure the amount of photosynthetically active radiation a light source will produce per second. A spectral graph shows the distribution of photons across the active spectrum. An example, courtesy of VividGro, is shown below. High PPF uniformity is one factor which contributes significantly to consistency in crop quality.
Photosynthetic Photon Flux Density (PPFD)
Photosynthetic photon flux density is a measurement of the average PPF over the lighting plane. PPFD says nothing about light uniformity. A high PPFD could be reported, but if the distribution is highly concentrated at the luminaire’s center, plants will be scorched in the middle of the canopy and stunted around the edges.
Lumens
Lumens (expressed as “L”) is the measurement of how much light the bulb puts out. Lumens are important in comparing an LED bulb to a traditional source. Comparing the lumens of an LED bulb to the lumens of a traditional one will help determine if an LED bulb will be bright enough to directly replace your traditional lamp.
Center Beam Candle Power (CBCP)
Center beam candle power measures the intensity of light at the center of a beam of light. This is an important measurement for spot and accent lighting. It often isn’t enough to only use the lumen output when determining if a lamp will be bright enough. It is possible to have a high LUMEN output, but a low CBCP.
Efficacy (lumens per watt)
Efficacy is a ratio of how many lumens are produced (how much light) per watt of energy consumed. The higher the efficacy ratio, the more efficiently your product is performing. Typically, you shouldn’t settle for less than 70lu/watt, and some LEDs are over 100lu/watt. Power factor is another measure of efficiency. The lower the power factor, the more current is wasted by the luminaire within the circuit. Look for a power factor of at least 0.9.
Color Temperature (CCT)
Correlated Color Temperature is a numerical value that indicates the color of light a particular fixture or bulb will emit. A low number indicates warm light. Think, fireplace or candlelight quality (red and orange hues). A higher number indicates a cooler light like daylight and hospital lighting (whites and blues). Standard ranges are around 2700k on the warm side to over 5000k on the cool side.
Color Rendering Index (CRI)
CRI is color rendering index, which measures a light source’s ability to reflect colors accurately. Low numbers would be in the 40’s while 100 would be perfect.
Light Distribution – Angle of View
Light distribution (sometimes reported as angle of view or beam angle) refers to how the light intensity diminishes on a plane parallel to and below the luminaire. The angle of view is normally defined in degrees – °. LEDs are measured so that the line along half the viewing-angle from directly forward is half the brightness as at directly forward. Today’s LEDs have a much wider angle of view than previous models.
A wide angle of at least 120° is considered appropriate for cannabis when growing using 4’x4’ or 5’x5’ tables. In practical applications, this plane would be representative of the crop canopy. If the maximum light intensity is directly below the center point of the luminaire, one-half of the beam angle in any direction connects a line from the luminaire’s center point to the parallel plane where the light intensity will be 50% of maximum.
LED Colors
The color of an LED is obviously of major importance when choosing an LED. LEDs are highly monochromatic, emitting a pure color in a narrow frequency range. The color emitted from an LED is identified by peak wavelength (lpk) and measured in nanometers (nm ).
Peak Wavelength
Peak wavelength is a function of the LED chip material. Although process variations are ±10 NM, the 565 to 600 NM wavelength spectral region is where the sensitivity level of the human eye is highest. Therefore, it is easier to perceive color variations in yellow and amber LEDs than other colors. LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels
Current / Voltage Specification
LEDs are current-driven devices and the level of light is a function of the current – increasing the current increases the light output. It is necessary to ensure that the maximum current rating is not exceeded. This could give rise to excessive heat dissipation within the LED chip itself which could result in reduced light output and reduced operating lifetime. Most LEDs require an external series current limiting resistor. Some LEDs may include a series resistor and will state the overall operating voltage.
Reverse Voltage
LEDs are not tolerant to large reverse voltages. They should never run above their stated maximum reverse voltage, which is normally quite small. If there is any chance of a reverse voltage appearing across the LED, then it is always best to build in protection into the circuitry to prevent this.
Wattage
Wattage measures how much energy a lamp needs to light up. While there are other benefits to LED lighting over traditional lighting, their reduced wattage consumption is among their biggest advantages.
Rated Life
Another key advantage LED’s have over traditional lighting is how long they last. There are LED bulbs that can replace a 4,000-hour halogen lamp and last up to 50,000 hours. Remember, this means that it should be at 70 percent brightness after 50,000 hours.
The rated life of an LED is how long it is intended to operate before reaching 70 percent of its original brightness. With traditional light sources, the rated life is the length of time the product is expected to operate before burning out. This is set by listing the number of hours it takes to burn out. LED’s, however, don’t typically burn out. They slowly dim over time. An LED’s rated life is therefore when the lamp is expected to be 30 percent dimmer than it was when brand new.
Safety – UL listing
Underwriters Laboratory is an independent testing laboratory dedicated to product safety. UL has no vested interest in any product but instead tests to nationally-recognized standards and vets product performance claims.
Significant time and money investment are required by a company to obtain the UL mark on their luminaires, so make sure you only purchase UL listed products.
These are some of the main LED specifications that are likely to be highlighted in the datasheets. Before choosing a particular LED, it is necessary to look at all the parameters to make sure it meets the requirements of your specific grow house application.