An artificial source of light is supplied when growing indoors. Plants require a certain colour spectrum of light to promote optimum levels of photosynthesis. A plant in a vegetative state will perform best under a blue spectrum of light, while the same plant in flower will perform best under a red spectrum of light. Light spectrum colours are measured in nanometers. Intensity of light is measured in lumens.
Fluorescent lamps are primarily used as a light source for seedlings and cuttings due to their low lumens per watt rating. There are a wide range of fluorescent tubes available, categorized by wattage, length, colour temperature and colour rendering index. The best suited tubes are those with a colour temperature of 5000 or greater, which is perfectly suited for early root and leaf development.
High Intensity Discharge or HID is the term for a gas-discharge light. Among the common types of HID lights are mercury vapor, low and high pressure sodium and metal halide lamps (see below). HID lamps produce light by sending an electrical charge or ‘arc’ between two electrodes and through an ionized gas which is housed inside the bulb.
HID lights require ignition which is usually provided by a voltage pulse or a third electrode inside the bulb. Once lit, the electrical arc begins to evaporate the metal salts inside the bulb, increasing the luminous power of the bulb and improving lighting efficiency. HIDs require a warm-up period because the lighting intensity is dependent on material inside the bulb evaporating into ionized gas.
As a HID light heats up, it requires additional voltage to operate. Voltage requirements in HID bulbs are managed by ballasts. As the HID light ages, more and more voltage is required to produce the same amount of light until eventually the voltage exceeds the fixed resistance provided by the ballast and the light fails. HID lights become less and less efficient over time because they must use more and more voltage to produce the same lumen output as the light degrades.
HID lamps are suitable for both the growth and flowering stages of the growth cycle. HID lamps have a higher lumens per watt rating than fluorescent lamps. HID lamps produce light by passing electricity through vaporized gas under high pressure. They require a precise starting technique provided through power boxes and special fittings and fixtures that house the lamps. Due to their high output, a large amount of heat is produced for every watt, so adequate ventilation is a critical when using HID lamps.
Metal Halide lamps create an abundance of blue light that makes them suitable for vegetative growth. Blue light promotes short internodal spacing and therefore excellent plant structure.
High Pressure Sodium lamps produce more yellow/red light which stimulates hormone production and a higher flower to leaf ratio. Therefore, they are perfectly suited for the flower stage of the growth cycle. HPS lamps have a higher output and last longer than Metal Halide lamps.
LED stands for Light Emitting Diode. A diode is an electrical device or component with two electrodes through which electricity flows. Diodes are generally made from semiconductive materials such as silicon or selenium. When current passes through the semiconductor material the device emits visible light.
LEDs have an extremely long lifespan relative to other lighting technology (including HID). New LEDs can last 100,000 hours or more. The typical lifespan for an HID bulb, by comparison, is 10-25% as long at best (10,000 – 25,000 hours).
LEDs are extremely energy efficient relative to other lighting technology. There are several reasons for this; they waste very little energy in the form of infrared radiation, they emit light directionally and they do not require additional voltage as they age.
LED technology has progressed significantly in the last few years. The new generation of LED panels blow every other lighting system out of the water! LEDs put off less heat, use less power, are smaller and more durable and they last longer than other forms of lighting. LEDs also offer a full spectrum of light, and some models even allow spectrum variability.
We have performed comparison tests using an ARCEYE LED 450w board vs a 600w/400V top of the range digital ballast. The 600w digital ballast produced an average of 0.5 grams per watt vs the ARCEYE 450W which smashed it out of the ballpark at a whopping 1.5 grams per watt!
LED is available in a wide range of customisable color temperatures. LEDs generally have better color temperature options than HID.
HID lamp color temperatures are determined by the materials used to generate the light. High Pressure Sodium and Metal Halide utilize different chemical compositions to generate specific light color temperatures.
CRI for LED is highly dependent on the particular light in question. That said, a very broad spectrum of CRI values is available ranging generally from 65-95.
Typical CRI values range from extremely low in the case of low and high pressure sodium lamps (0-25) to moderate in the case of metal halide lamps (60). Some HID lights may reach CRI as high as the mid 90s.
LEDs turn on and off instantly. They produce steady light without flicker.
HID lights require a warmup period. They may also flicker or cycle on and off as the bulb reaches the end of its useful life.
LEDs are very easy to dim. They do this by either lowering the forward current or modulating the pulse duration.
HID lights can be manually dimmed using a ballast, but the process changes the voltage input to the light and can consequently alter the light characteristics. In some cases, dimming can cause the light to prematurely expire. Without a ballast, HID bulbs cannot be dimmed.
LEDs emit light for 180 degrees.
HID is omnidirectional meaning it emits light for 360 degrees.
WINNER: Depends on usage.
LEDs are very efficient. Typical source efficiency ranges 37 and 120 lumens/watt. LEDs have exceptional system efficiency (the amount of light that reaches the target area after all losses are accounted for). Most values for LED system efficiency fall above 50 lumens/watt.
HIDs are very efficient compared to CFL lights (120 lumens/watt source efficiency). However, they are inferior to LEDs because their system efficiency is much lower (<30 lumens/watt) due to losses associated with omnidirectional light output and the need to redirect it to a desired area. By far the most efficient HID variant is the High Pressure Sodium lamp whose source efficiency can range from 100-190 lumens/watt.
LED efficiency drops as current increases. Heat output also increases with additional current which decreases the lifetime of the device. The overall performance drop is relatively low, however, when compared to HID.
HID lights also experience efficiency losses as the device ages and additional current is required to achieve the same lighting output. Efficiency losses are greater and the degradation time shorter in the case of HID.
LEDs fail by dimming gradually over time.
HIDs exhibit an end-of-life phenomenon known as cycling where the lamp goes on and off without human input prior to eventually failing entirely.
LEDs emit very little forward heat.
HIDs emit a lot of heat and often need to be vented.
LED lifespans are variable but typical values range from 25,000 hours to 200,000 hours or more before a fixture requires replacement.
HID lifespan values range from 6,000 hours to 24,000 hours before a bulb requires replacement. Note: sometimes HID lights need to be changed out before the end of their useful life to preempt serious degradation effects like color changes or cycling.
LED lighting has relatively high initial costs and low lifetime costs.
HID is relatively cheap to purchase but it is relatively expensive to maintain.
LED has virtually zero maintenance costs.
HID bulbs require regular relamping and ballast replacement.
LED light costs are getting lower, but they are still more expensive than HID options.
HID bulb costs depend on the specific type of HID light, but most HPS lights are relatively cheap.
LEDs are solid state lights (SSLs) that are difficult to damage with physical shocks.
HID bulbs are quite fragile. Perhaps more importantly, broken HID bulbs require special handling and disposal due to the hazardous materials present inside of many lights.
LED fixtures are wide and flat and don’t take up much space in the grow room.
HID bulbs require venting and a ballast which takes up quite a lot of space in the grow room.
LEDs have virtually no warm-up time. They reach maximum brightness near instantaneously.
HIDs require a warm-up time that varies depending on the light.
LEDs – Often 5-10 years
HPS – typically 1-2 years