Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs.
High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in plants to increase flowering/budding in plants. They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.
Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum. If a gardener were to start a young plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most plants would grow up thin and lanky and in no time you will have to prune your plant back before it grows into the light fixture. The exception to this is using HPS grow lights in a greenhouse or in conjunction another light source that emits light in the blue spectrum. Light sources that have a high output in the blue spectrum like sunlight and MH grow lights offset any stretching caused by HPS bulbs.
Until recently, fluorescent grow lights have had a low output and have been too big and bulky to be of much use as a grow light for anything more than starting seedlings. CFL and T5 full spectrum fluorescent lights have changed that. At 75 to 90 lumens per watt, these lights are energy efficient and extremely effective especially when used in numbers. Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights. This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant. It is recommended that these lights be placed no more than a couple feet from the plants for best results. 2700k to 3000k bulbs provide higher output in the red spectrum which promotes flowering. 5000k to 6500k bulbs are full spectrum with much of the light in the blue spectrum which promote overall green plant growth. ,
The standard T12 bulbs full spectrum tubes are fine for starts and seedlings and are popular for growing low-light plants like herbs and African violets. These lights are inefficient and are be replaced with high efficiency T5 lights which are a better light source for flowering and budding applications as well.
Horticultural lighting systems allow you to extend the growing season by providing your plants with an indoor equivalent to sunlight. This is a great advantage for those of you who appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting is also a great way to jump-start spring by starting your seedlings months ahead of the last frost. There are three main types of horticultural lighting systems.
The module highlights a general method of chemical analysis (chromatography - activity one) that is used in more high tech forms to determine the types and concentrations of fermentable sugars produced from cellulosic biomass. Activity two investigates from where plants get their mass. Producing ethanol from cellulose is difficult but does not compete with food production. Activity three in this module will help show students why it is important to measure the types and concentrations of the sugars produced.