Full Spectrum

The term full-spectrum was coined in the 1960s by photo-biologist Dr. John Ott to describe electric light sources that simulate the visible and UV spectrum of natural light Today there are many fluorescent lamps advertised as "full-spectrum." All fluorescent bulbs marketed as "full-spectrum" grow lights are tri-phosphor-coated. Until photo-biologist Dr John Ott began producing and selling the first "color-corrected" bulbs, all fluorescent lamps were halo-phosphor or deluxe halo-phosphor blends, which did not render the reds well. Tri-phosphor-coated lamps emit the visible light spectrum in spectrums from 2700 K to 6400 K. They simulate colors by mixing the three colors associated with the three cone types in our eyes "specially formulated to replicate all the wavelengths in the visible spectrum."

The term "full-spectrum" has been successful to help sell overpriced lights. Now the market is rampant with hype about the lights. Resellers purchase tri-phosphor bulbs from manufacturers and market them as "Grow Lites." Major lamp manufacturers do not sell tri-phosphor-coated lights as "lull-spectrum."

Spectrum GroLux is designed to supplement natural light and covers the blue to far-red regions. Westinghouse has the AgroLight that produces a very similar spectrum to the sun. Warm White and Cool White bulbs used together make excellent lamps to root clones.


Kelvin Temperature

Warm White

2700 K


3000 K


3500 K

Cool White

4100 K

Full Spectrum

5000 K


6500 K

Fluorescent bulbs are further classified by diameter and come in the sizes Tl 2 (1.5 inch [5 cm]), T8 (1 inch [3 cm]), T5 (0.625 inch [1.5 cm]) and CFL (see section below "Compact Fluorescent Lamps"). The T12 uses old-fashioned magnetic ballasts. The T8 and the T5 (technically CFL's) use electronic ballasts. Growers prefer slimmer T8 and T5 bulbs with electronic ballasts because they run cooler, electricity cycles faster, and lights do not flicker.

The average lumen output of a 40-watt T12 is 2800 lumens, about 68 lumens per watt.

A 32-watt T8 bulb yields 100 lumens per watt and cranks out 100 average lumens.

A 54-watt T5 throws 5000 average lumens, which means it produces 92 lumens per watt.

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