This is the most misunderstood concept when it comes to UV lamps, and I want to share 25 years experience and set the record straight. I've even had, lets just say a very famous cannabis author and activist, screaming in my face over this issue while at a trade show, so obviously there is a lot of heat when it comes to this topic. Let me shine some light on the topic.

Lets start by defining what these really are, assuming we are talking about lamps that are around 4 foot long. T12 means the lamp is 1.5" in diameter. A T8 is 1" in diameter. A T5 is 5/8th" in diameter. The "T" number is simply the diameter of the lamp, in 1/8" increments. This is true for all lamps, not just ultraviolet lamps.

A 4 foot T12 is known as a F40T12 and uses 40 watts. A 4 foot T8 is a F32T8 and uses 32 watts. A 4 foot (46" really) T5 is usually known as a F54T5 although there are also F27T5s. In the growing market, almost everyone uses the F54T5, which uses 54 watts of power. This F54 puts the most power in the smallest package, which is both a good and bad thing, as we will cover later.

People are under the impression that the smaller the diameter, the more efficient the lamp is. This is generally true for visible light frequencies, but ultraviolet is not the same as visible light in several key ways.

Circumference

The circumference of each lamp is key and affects things like heat dissipation, the amount of phosphor that can be used, and whether or not an internal reflector can be used. Here is the breakdown between the three lamp sizes using π/r² formula:

T12= 1.5" diameter = 4.71" circumference
T8 = 1.0" diameter = 3.14" circumference
T5 = 0.625" diameter = 1.96" circumference

This is the outside diameter, not inside, but you get the point. There is a LOT more surface area with the T12, which has 2.4 times the surface area of the T5, yet the bulbs are about the same length. The T12 will run much cooler inside because it has more surface to dissipate heat to, making it last longer. Heat and cycling are the two things that kill any fluorescent bulb, even more than hours of use. A T12 will also have more phosphor because it has over twice the area to coat the phosphor. This is a big deal when you are talking about UV and not visible light.

Reflectance

With any fluorescent lamp, half the light created wants to go away from where you want it to go. It shines light in all direction. Most people are not aware, but the "reflectors" on the light fixtures you buy will NOT reflect UV. They will reflect visible light, but not higher frequencies like UVB. Trust me, I've tested dozens of different models and paint types over the year, back when I designed tanning beds even. Polished aluminum (even aluminum foil from your kitchen) does a fair job of reflecting UVB, around 50% of the light, but it is no where near as efficient as a built in reflector. The larger bulb diameter (T8 and T12) make it possible to use a RUVA design, which is a built in reflector. All Solacure T8s and T12 use this design, and I think we are the only ones who do. It costs more, but here is why it is the smartest money you can spend when designing a bulb:


This is a cutaway view of two lamps. To the left is a regular lamp, the right is a lamp with a RUVA reflector system. The reflective material is poured in the tube before the phosphors are added (shown as being blue here, but is actually white). By reflecting the UV before it even leaves the column of plasma, you get up to 50% higher UV on the end product. You can do this with T12 and T8 lamps. It CAN be done on T5s but is very expensive and the reflector also reflects heat and infra-red light, which lowers life and creates other issues. We can use our patented glass, the RUVA design, full spectrum UV phosphor blend and beat any T5 when it comes to actual THC results, plus the T12 will have around twice the life of the T5, making it a lot cheaper to operate.

Facts

If I convince you of anything today, it would be this: With regular visible light, you are fighting to get the most photons you can from a single tube, but that is not the case with UV. It isn't hard to make UV lamps that will kill the plants in a few hours, any fool can do it. For your own benefit, you need to stop thinking that T5 is automatically better for UV, it isn't. Smaller is fine, but it doesn't mean "more advanced" or "better", it only means "smaller". I've tested plenty of T5s, produced prototypes out of Germany from a manufacturer that specializes in these. I've worked with them 25 years, size doesn't indicate quality nor does it mean it is more technologically advanced. Raw UV power is easy to do, but getting a UV spectrum that will dramatically increase THC takes more effort. After all, you aren't buying bulbs for the fun of it, you are buying them for a single purpose: to increase THC and other resins.

The T8 is probably the best compromise in many way, and we have created a half dozen UV grow lights using T8s. Most OEMs are standardizing around the T8 for a reason: it produces plenty of UV, it produces a really nice spectrum that can double the results of a single phosphor T5, while using less electricity, thus generating less heat.

Advantages

What are the main advantages of a T5 over a T8 or T12? Well, they are smaller, this is true and that matters for some people, particularly in small grow situations. Plus there are existing fixtures you can drop a T5 into, assuming you already have those fixtures. If you don't already have spare T5 fixtures, that is kind of moot. They look "better". I don't know why, but some people think the small tubes look "cool" or more advanced. That might be good marketing, but physics tells us that they each are just different, not better. It is like comparing a car to a truck. What you are doing will dictate which is the better tool.

Finally

If I were growing (we can't in NC), I would be using the T12 Flower Power....I wouldn't give it a second thought. Yes, it is larger, but the spectrum is a beautiful thing, very sun-like in UVA and a full spectrum (but greatly increased) UVB output. They reach down to 280nm (all other lamps peter out around 300nm, the glass filters it out), and can operate from 25 to 100 watts. I would run it in pulse mode, 40-45 watts: 15 minutes on, 45 minutes off. And I would be getting 2 to 3 flowering seasons out of each lamp easily. The larger lamp produces less heat, last longer, uses less electricity, has a better spectrum, has more than enough UV power, has a built in reflector (Remember: painted reflectors in fixtures are useless for UV) and costs a little more up front, but is actually much cheaper to operate. That doesn't mean we don't produce other good lamps, this is just what I would do because I'm would be more focused on results than anything else.

What makes a product good isn't the size or format. All LEDs are not automatically better than high pressure sodium or metal halide, for instance. Many are. You already know this. The same is true for UV lamp size. There are advantages and disadvantages to the difference sized UV lamps. If your goal is to get the highest THC (or jump up the CBD if you run in pulse mode), then forget size and instead focus on the spectrum, the output, the quality of the lamp itself. Otherwise, you are going to spend years testing gimmicks that never live up to the promises.

This is why we offer the larger size tubes, why we give people a money back guarantee, and why we just grin when someone claims "T5s are better than T12s". We know it isn't true; they are just different.

Dennis Brown