What are HID Grow Lights? Grow Lamp Basics | EYE HORTILUX™
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 Image of HID grow lights from EYE HORTILUX, who also make ceramic metal halide grow lights.

HID Grow Light Basics

What are HID Grow Lights?

HID lights are High Intensity Discharge lights.

HID lamps, or light bulbs, are high-powered light sources. They include Metal Halide lamps and High Pressure Sodium lamps. EYE HORTILUX™ HID lamps are manufactured specifically for indoor horticulture. They supply artificial light for indoor plant growth.

Unlike incandescent light bulbs, HID lamps do not have a filament. HID lamps are electrical discharge lamps. This electrical discharge is similar to the arcing of a lightning strike, only with much lower power and much longer duration.

Explore this detailed information about how grow lights work, the location of lamp components, and lamp terminology.

High Intensity Discharge (HID) lamps create light by heating up materials inside the arc tube. Metal Halide lamps, for example, heat up the scandium inside the tube.

In its atomic form, a scandium atom is composed of a nucleus surrounded by 21 orbiting electrons. For this demonstration we’ll focus on only three of the orbiting electrons.

spectral distribution

When electrical power is applied to the arc tube, free electrons (that are not bound to an atom) flow through the arc tube. Then they collide with other electrons that are bound to, and orbiting around, the Scandium atoms.

During this collision, a bound electron is knocked out of its orbit. It cannot escape the pull of the nucleus, and is drawn back. When the electron snaps back into its orbit, a release of visible energy occurs. This visible energy is called a photon.

The distance from the orbiting electron to the nucleus determines the energy levels of the photons created.

We record these energy levels, or wavelengths, on spectral distribution charts (also known as relative energy charts.)

The HORTILUX™ 1000W Super HPS


The HORTILUX™ 1000W BLUE Metal Halide

(Not Shown) The Fly Wire completes the circuit during start up of the lamp.

HPS Arc Tube

(Not Shown) A chemical dose, inserted into the ceramic tube which consists of mercury and sodium, interacts with the electrical arc to create the brilliant light.

Metal Halide Arc Tube

"Julian" Date Code

Date of manufacture reads: 236 11
Meaning the 236th day of 2011 = August 24, 2011

Monogram Color

A new lamp will have a BROWN monogram.  After ten hours of burn time the monogram will turn ORANGE.

Base Date Code is printed on the ceramic insulator for easy lamp traceability. When installing lamp, mark the month and year of installation by scratching through the letter and number.


  • Traceability - Field and Factory
  • If lamp is returned broken, date of manufacture can still be determined

common base

Environmentally-friendly lamps, or EN lamps, are designated by the Environmental Protection Agency (EPA.) The EPA uses a method called TCLP to determine if a lamp contains non-hazardous waste. To meet these strict standards, the bulbs must be completely lead-free, including the solder and glass. They must also contain reduced levels of mercury.


  • Meet ANSI/IEC base torque standards
  • Feature standardized EYE design to ensure quality.
  • Use EYE / Iwasaki US-Patented design

Plasma-Welded Eyelet is Lead Free.

solder lock
Old Solder Lock

improved lock Improved Weld Lock

different lightbulb shapes

Note: Bulb size or diameter (maximum) is expressed in an eighth of an inch (1/8") for one unit. For instance, a BT56 bulb is 56 eighths of an inch in diameter, or 7 inches in diameter. See ANSI C79.1 for a complete details on bulb shapes.

lamp dimensions
Maximum Overall Length (M.O.L.):
MOL is measured from the end of the lamp base to the top of the outer jacket.
Light Center Length (L.C.L.):
The distance from the light center to a specified reference point on the lamp.
The diameter is the maximum diameter of the glass bulb.
Maximum Overall Length (M.O.L.):
The distance between the ends of the bases.
Contact to Contact:
The length between contacts is the distance between the metal contacts which are recessed inside the ends of the bases.
Nominal Diameter:
The approximate diameter of the tube.

Lamps must be used in their specified operating positions in order to maximize lamp performance and longevity. Incorrect operating positions may also create the possibility of a lamp rupture.

It is imperative that users adhere to the specified operating positions and fixture requirements. The following chart shows the correct lamp operating positions based on the Position Code Letters. These letters are always presented in the lamp description.

Fixture Requirement Codes

  • O = Open fixture permissible. Lamps can be operated in an open fixture within the lamp's specified operating position limits.
  • S = Open fixture permissible with operating position restrictions.
  • E = Enclosed fixture required. Lamps must be operated in an enclosed fixture.

Lamp Operating Position Codes and Symbols

U or no code BU BUD
Universal (no limit) Base Up ±15° Vertical ±15 Base Up or Base Down
universal bud
Base Up or Base Down ±60 Base Up to Horizontal Horizontal ±15°
bud60 buh
HOR ±30 HOR ±45 HOR ±60
Horizontal ±30° Horizontal ±45° Horizontal ±60°
hor30 hor45

Metal Halide Lamp Monograms

High Pressure Sodium Lamp Monograms

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EYE HORTILUX® offers grow lamps and ballast for indoor gardening applications. Our grow lamps are made in the U.S.A.

Made in America
  • HORTILUX® is a trademark of Iwasaki Electric Co.,
    and is registered in USA and Japan.