LED Lamps

This is the first part of a two part article about LED lamps. The second article will run next issue of Soft Secrets.

This is the first part of a two part article about LED lamps. The second article  will run next issue of Soft Secrets.

You can see each LED bulb soldered onto the white plastic panel. The bulbs must be covered to protect circuitry from moisture and malfunctions.

LED lamps are everywhere. You see them in stop lights, flashlights and household lighting, Christmas tree lighting, etc. The technology has come a long way since it was developed in the early 1960s, when LEDs were found in appliances and generated a faint 0.001 lm/W. New LED technology is advancing rapidly and they are becoming much brighter and more electricity efficient. LEDs are available across the visible spectrum, and from ultraviolet through infrared. Gardeners are successfully using LED lights to cultivate medical cannabis. But, there are so many different types and so much “sales” information is available about LED lamps that it is difficult to understand which specific LEDs work best as a light source to grow medical cannabis.

LED (light-emitting diode) lamps use solid state semiconductor energy to produce light. The technology is similar to that found in the computer circuitry. They do not use filaments found in incandescent and tungsten halogen bulbs, or gas which is used in HID, fluorescent, and compact fluorescent bulbs. LED lamps generate very little heat and are rated for regular household current—120 V and 240 V.

Outdated LED lamps that produce less than one watt are not as bright as new 1, 2 and 3-watt bulbs. Also some bulbs of the same wattage are brighter than others. See “Brilliance” below.

Rather than a ballast, a series of resistors or current-regulated power supplies is necessary to deliver precise voltage and current to operate most efficiently. The power supply can be decreased to dim lights. Some bulbs have a dimming range of 20-100 percent. The necessary hardware is hard-wired and soldered into a small (circuit board) fixture that is connected to a power supply. When purchasing a fixture, consider how bulbs will be replaced. Individual clusters of bulbs that can be replaced within fixtures are the most economical and practical.

If ambient temperatures in the operating environment climb too high, LEDs overheat and “droop” producing less light. Similar to solid state computer chips, LED bulbs fail sooner when overheated over time.

LED bulbs are driven in miliamperes (mA). Some LEDs are driven at lower mA to increase efficiency. The science and data behind all the circuitry is more complex than the scope of this book. The best way for average medical cannabis gardeners to discern the brilliance of bulbs or a fixture is to measure light output with a light meter.

LED lamps are used for propagation, vegetative and flowering in cannabis horticulture, as well as some experiments with inter-lighting in greenhouses. They are NOT a replacement for HPS in greenhouses.

Cost

New technology is expensive and cost has been one of the biggest impediments to LED light use in gardens. They have been too expensive, dollar per lumen. Bulbs in 2010 were producing from 40-60 lm/W. This year, 2012 they are producing more than 10 percent higher lm/W readings. The technology is changing every few months and it is difficult to keep up with it!

Prices range from $40 for a 15-watt incandescent retrofit bulb to $600 for a 300-watt fixture. In 2009 a 90-watt LED fixture cost $600, about three times more than in 2012. Today a small bulb costs about $2.50 per watt and a large fixture costs about $2.00 per watt. You can purchase HID light at the rate of $0.35 per watt. The good news is that LED technology is improving and production costs are dropping quickly.

The Hydro Grow LED is manufactured with lenses that increase light output up to ??? percent. (see graph). The technology pays for itself with electric power savings over the long term, after the initial cost of the fixture, $2,199 is paid.

CFL that produces 800 lumens uses less than 15 watts and costs about $75 of electricity per year. According to manufacturers, LED bulbs that produce the same 800 lumens draw less than 8 watts of power and cost about $30 per year, and last 50,000 hours or longer.

LEDs that produce UV light are too expensive to manufacture to be practical to use in the garden.

Brilliance and Spectrum

The best way to decipher LED bulb output within the following equation – amperes x voltage = watts (Ohms Power Law), otherwise light output can become quite complicated and confusing. For example, a 3-watt LED that runs at 350mA (mA = milliamps) yields 1 (one) watt of light.

Depending upon manufacturer, modern LED bulbs produce from 40-60 lm/W (lumens per watt). New bulbs produce more than 200 lm/W. Cree Incorporated announced a LED lamp in 2011 that generates 208 lm/W, in early 2012 the bulb was not yet on the market. Brighter and brighter LED bulbs are continuing to be developed.

But, the small LEDs heat up quickly and loose efficiency, which is light energy converted to heat beyond a specific operating temperature. The operating temperature is a function of electric current (mA) input.

Humidity is detrimental to circuits. LED circuitry is exposed (foto) and must be protected from humidity to avoid corrosion. The LEDs must be enclosed to isolate them from exterior humidity.

The optimal temperature for each color of LED ensures an accurate rendering of color spectrum.

At maximum temperature or too high of a temperature the lamp will fail. That is, if too much current is run through the little LEDS they get too hot, become inefficient (light energy is transformed into heat) and they fail, burn out.

LED bulbs are designed to focus light. One innovative company, Hydro Grow LED, takes advantage of the ability to focus the light emitted and directs it with a lens, just like beam of light is “projected” in a movie projector. The light output is not only concentrated and intensified, it is increased. Their fixture couples special little lenses for the LEDs to increase light output.

Once manufactured, LEDs are tested for brightness and sorted into different bins. Some LEDs are brighter than others and fetch a higher price. For example, LEDs are sorted into bin 1, 2, 3. The LEDs in bin 1 are brighter and more expensive than the next brightest in bin 2. Those in bin 3 are the least bright.

LEDs come in a variety of spectrums and are unique in that they are available in monochromatic wavelengths producing specific nanometer wavelengths and colors. LEDs with different spectrums can be grouped together to form a spectrum that is perfect for plant growth.

LED technology allows manufacturers to literally dial in the spectrum of fixtures to produce incredibly high PAR ratings. This point alone makes them more efficient per watt. But the PAE rating efficiency is not rated in lumens as lamps that are designed for human vision.

NOTE: The spectrum of each LED bulb may also dictate the brilliance, light output.