Any part of the plant that is further away then 1-2 feet from the fluorescent grow lights is not getting an optimum amount of light, especially in the flowering stage when plants need a lot of light to produce buds.
However, you can use either type of lights during either stage and still get good results. People also use "Daylight" (5000K) bulbs with success.
For optimal results, for vegetative growth choose fluorescent light bulbs that are labeled either as "Cool White" or "Cool" colored (also labeled as "6500k" colored).
In general, I recommend changing to stronger grow lights like LEDs or HIDs for the flowering stage because they will usually give you double or more yields/watt of electricity. Unless you keep your plants very small, they will need more light to produce buds than a fluorescent light can usually produce. If you're in a dire situation where your plants have grown too big and you can't afford to get a different type of light, you can supplement your fluorescent tubes with additional light, for example you could supplement their light with a few CFL(compact fluorescent light) bulbs wherever you notice any "shadowy" areas. This is only a minor fix – the real fix is to grow very short plants or upgrade to a bigger light for the flowering stage.
A few years ago, growers usually only used fluorescent tube lighting as a supplemental light for cannabis plants, or for young seedlings and clones only.
T5 fluorescent grow lights are energy efficient and provide consistent levels of light to all of the plants within their reach. Whether you’re already up and running with your T5 fixtures, or are just starting out, this article contains helpful advice.
Choosing the Right T5 Grow Lights
You are almost ready to go—all that’s left is figuring out the right light cycles, and then you can turn on your lights and start growing. A light cycle refers to how many hours you keep the lights turned on for and for how many hours you leave your plants in the dark. Light cycles are used to simulate night and day. Outdoor plants get a certain amount of hours of light and dark to grow properly, and you need to simulate these conditions indoors, too.
Now that you have selected the right fixture and bulbs, it is time to set up your grow lights. The first thing you need to think about when setting up T5 grow lights is the height, or how high above plant canopies you are mounting your fixtures. Although T5 lights are famous for emitting very little heat, this doesn’t mean you can put the bulbs an inch above plant canopies, as this distance will still damage the plants.
First, they may have a slightly shorter average lifespan than T8 bulbs, as explained by the fine folks over at the NLPIP. While this may not be a great cost concern for small grows (with each T5 bulb costing between $2.50 to $12), it may be something you want to consider if planning larger-scale indoor grow operations.
Coming one generation before T5 bulbs, T8 LED grow lights are slightly less energy efficient – but more likely to fit into a wider variety of housings without having to make any modifications. Whereas T5s cannot be interchanged with previous generations, T8s can be.
T8 Grow Lights Explained
Because the T8s give off less heat and less light, they are in fact more suitable for these early phases. If you were to use a brighter, hotter T5, you would run the risk of scorching the plants or upsetting their biological rhythm necessary for the early stages of growth.
From there, you could consider transferring your (now hardier) plants to a brighter, warmer lighting situation – without fear that they will be damaged.
Downsides of T8 Grow Lights
The most common of all T style bulbs, T8 grow lights are a tubular style of lighting with a diameter of 1 inch.