Lighting

Introduction
In hydroponics, there are three major players in lighting:


 * 1) HID-lighting
 * 2) Flourescent lighting
 * 3) LED lighting

HID
HID lighting is the most common form of lighting for hydroponics. HID light. HID lighting is very wavelength specific. It is necessary to use different bulb types or mixed bulbs to get a similar spectral distribution to sunlight. HID lighting requires a ballast that boosts the normal voltage in homes to the high voltages required to excite the gases in the bulb.

The life of an HID bulb...

Advantages:
 * Superb brightness
 * Generally accepted primary lighting technology for indoor hydroponics

Disadvantages:
 * Cost: They are more expensive than other types of lighting
 * Power: They use more wattage than both fluorescent and LED
 * Heat: The lamps must be cooled, and the heat must be conducted out of the grow room
 * Space: More room must be placed between plants and the lamp
 * Weight: The traditional and cheaper coil ballasts are very heavy
 * Incompatibility: Most MH ballasts are not compatible with HPS and vice-versa

Fluorescent
Fluorescent lighting is similar to HID in that it uses excited atoms of gas, but instead of the gas directly emitting photons of visible light, flourescent lighting works by exciting mercury vapor so that it emits photons of UV-band light that is outside of the visible range. To make this light energy useful, the inside of the bulb is coated with phosphorous compounds that emit different wavelengths of light when struck from the inside by the UV photons.

One of the main advantages of fluorescent lighting is its high efficency vs. low power usage. Fluorescents also run cooler, so they can be passively cooled and can be placed closer to foliage without risk of damage. Fluorescents also emit very broad, balanced light, very similar to daylight. Fluorescents are also cheaper than HID.

The life of a flourescent bulb is limited, because a compound is used on the ends of the bulbs to help with ignition. This compound is consumed while the bulb is running, and this is what blackens the ends of a fluorescent tube.

Advantages:
 * Suited to setups that are longer than they are wide
 * Cheaper than HID
 * Cooler that HID
 * Allow for more compact setups because plants can be closer to bulbs
 * Good spectrum

Disadvantages:
 * Limited life (tubes are expected to last 6 months before light output for photosynthesis it too low)
 * Lower light output as compared to HID
 * For plants that flower or fruit, the lights may not provide enough strength

LED
LED is the newcomer to hydroponics. LED light, like laser light, is specificially marginalized around a single frequency, so most LED light panels contain a proportion of different colors to populate the spectrum that plants use.