There are many types of fluorescent grow lights available but lately a commonly asked question is about the difference between T4 and T5 light and frankly which is better. So with this post I will try to answer this question as best as I can, even though the answer definitely won’t be unequivocal, because different people prefer different lights.

To better understand T4 and T5 lights we need to learn a bit about them. The letter T of the name of these lights represent the fact that these bulbs are tube shaped. But the number that is placed alongside the letter marks the diameter of that particular bulb measuring in eights of an inch (~38.1 mm).

Here also we can see the first and probably one of the biggest differences that T5 and T4 bulbs have, meaning that one of them – the T4 light – is slightly slammer in diameter. If the T5 bulbs are 5 eights of an inch in diameter (about 15.9 mm), then T4 bulbs are 4 eights of an inch in diameter (about 12.7 mm).

The next difference between T4 and T5 grow lights are their efficiency or their watt consumption and lumen output. Although there can be seen some difference in wattage meaning that the T4 lights are a bit more efficient because on average T4 bulb around the size of 2 ft T5 bulb will consume 20 watts while T5 will chew up 24 watts, the T4 bulbs will emit much less lumens so with T4 bulbs you plants will get less light for just 4 watts an hour less in electricity consumption. Moreover, T4 lights still don’t have regulated sizing, which means that you will have to go through many different sizes to choose the right one for you, while with T5 lights there are two main sizes – 2 feet and 4 feet bulbs – that make your decision much easier.

One thing that the T4 is superior over T5 lights is heat emission. Less watts consumed equals less heat produced so the T4 lights will keep cooler than T5 light, although T5 bulbs by themselves don’t get that hot so don’t let this fact make you reconsider buying T5 lights.

T4 bulbs also tent to be harder to find especially in stores or main internet websites for fluorescent lighting. Which begs to question is it worth to make your life harder and buy hard to find lights when there is option of T5 lights that are very easy to find and work similarly if not better than T4 bulbs.

Overall I tend to favor T5 bulbs over T4 lights mainly because they are great at giving plants the light they need, as well as among T5 lights there is established system that don’t confuse me in terms of bulbs size, wattage and lumen output. Bu like with all things you might find that T4 bulbs work better for you, so choose the bulbs that live up to your expectations and needs.