purple haze weed

One lumen per square foot is equal to one foot-candle, which is a term that describes the density of light that reaches a surface. Lumens are not a good measure of lighting for plant growth because they measure light visible to the human eye, but many bulbs will talk about their efficiency as lumens per watt of energy consumed. Lumens can also help to describe the life expectancy of a bulb, they are expressed as lumens per watt (LPW).

As light bulbs are used, the initial lumens will decrease. The life expectancy of a bulb is reached when lumens have dropped by 50%. High intensity discharge (HID) lamps have a life expectancy of 10,000 to 20,000 hours, and LEDs can last up to 50,000 hours. The “whiteness” of a light is measured by its color temperature in units of Kelvin (K). Light with a lower Kelvin rating has a yellowish tint, and light with a higher Kelvin rating has a bluish tint. In photomorphogenesis plants respond to colors in the light spectrum by altering their growth patterns. Seed germination and the switch from vegetative growth to floral growth are two important photomorphogenic reactions. Natural daylight has a color temperature of 5000 K to 5800 K. Natural visible light color perception can vary based on weather and season, but this is not to be confused with the electromagnetic spectrum light colors which do not change.

A light bulb that is identical in color to natural daylight would be rated as a 100 on the color rendering index. “Natural sunshine” fluorescent lights have a broad spectrum of peaks, where yellow and conventional fluorescent lights have just a few wavelength peaks around 540 nm and 630 nm. Full spectrum lights will emit all colors of the visual light spectrum from 400 nm to 700 nm. The “T” indicated that the bulb has a tubular shape, and the number indicates the diameter of the bulb. T5 bulbs make good grow lights because they are very efficient and come in a wide range of colors. T5 bulbs cover a grow space around 2x4 ft, additional coverage can be gained by use of multiple bulbs wired together in a “daisy chain”. PLL T5 bulbs are “U” shaped and can provide the efficiency of a tube bulb in a more compact space. Fluorescent lights plug into a ballast that regulates the electrical current flowing into the bulb to ensure it is supplied at the correct voltage. There are three main types of ballasts: preheat operation, rapid start operation, and instant start operation. Preheat operation is used mainly for bulbs under 30 watts, and is more energy efficient than rapid start operation. Rapid start operation is the most popular fluorescent ballast operation mode. This is the mode where the stereotypical fluorescent light flicker occurs. Instant start operation is more efficient than rapid start, but instant and preheat start operation will reduce bulb life. Compact fluorescent (CFL) bulbs are more efficient than traditional fluorescent bulbs and they can be screwed in to a regular (E27) light socket. CFL bulbs come in a range of brightnesses, from 13 watts to 300 watts. They can also be purchased in different colors such as warm spectrum bulbs (2700K) or cool spectrum bulbs (5000K to 6500K). Light Emitting Diodes (LED) grow lights have gained popularity because they can be customized to emit only the most productive wavelengths for plant growth. They can be placed closer to the canopy of a cannabis crop because they do not emit as much heat as high pressure sodium lamps or metal halide lamps. Heat sinks in the LED light housing help them dissipate heat well. LED lamps consist of several small lights in a grid, called an array. The LED driver functions like a ballast and regulates the input power, the driver also protects the light emitting diodes from voltage fluctuations as they heat up and age. The diodes of an LED light are covered and sealed in by a lens. The qualities of the lens can influence the viewing angle of the light. Viewing angle refers to the pattern the light disperses in. High intensity discharge bulbs and fluorescent bulbs have a viewing angle of 360°, but LED grow lights typically have a 120° viewing angle. Full spectrum LED lights can come with 2 settings, a red setting and a blue setting.

The blue setting will support vegetative growth in cannabis, and the red setting will support flowering. Full spectrum LED provides 730 nm (IR), 660 nm, 630 nm, 610 nm, 580 nm, 460 nm, 430 nm, and 410 nm (UV) light wavelengths.

Growers usually need LED grow lights for cannabis that have 32 watts per square foot of space, or about 32 watts per plant. Incandescent bulbs are very familiar light bulbs that are used in homes.


Get in touch