Key Takeaways
- T25 vs T100 tritium watch ratings are about quantity, not brightness: the number tells you the most tritium the whole watch can hold, shared across every tube.
- A T100 watch can hold up to four times the tritium of a T25. More tritium in a tube makes that tube glow brighter.
- Brighter isn't automatic. Tube size, how many tubes there are and colour all change what you see, and a green T25 can look brighter than an ice blue T100.
- Across our range, the MX10 and every Hawk except the Hawk Nightfall are T25. The Alpha, Alpha Z and Hawk Nightfall are T100.
- Choose by how you work in the dark: T25 for a low, discreet glow, T100 for the quickest read in full darkness or underwater.
We sell both T25 and T100 tritium watches, so we often get asked what the difference is between the two and which is better.
Firstly, what is Tritium illumination?
Tritium, also known as super-heavy hydrogen, emits electrons. When these electrons hit a phosphor coating, they create a light that can last up to 20 years.
When this Tritium powered illumination is sealed inside a glass tube, it is known as a GTLS (Gaseous Tritium Light Source). Full details on how tritium glows inside a GTLS tube.
Tritium illumination is widely regarded as the world’s best and most reliable form of watch illumination. That is why we use it in every NITE watch. Every tube we fit comes from mb-microtec in Switzerland.
So, what’s the difference between T25 and T100 tritium watches?
All watches with tritium illumination carry a “T” rating. This T rating refers to the total watch tritium content which is measured in millicuries. Watches with a T25 rating contain up to 25mCi of tritium, and watches with a T100 rating contain above 25mCi and up to 100mCi.
A T100 watch can hold up to four times the tritium of a T25 watch.
But the individual tubes in a T100 rated watch aren’t necessarily any brighter than those in a T25 watch. It means there is more tritium content in the entire watch.
T25 and T100 side by side: same layout, bigger tubes on the T100.
Is T100 actually brighter than T25?
Often, yes. Not automatically, though, and not by a fixed amount.
The T rating is a ceiling on the whole watch. It isn't a measure of light. That tritium is shared out across every tube on the dial and hands.
More tritium in a tube does make that tube glow brighter. Give a T25 and a T100 watch the same tube layout. The T100 will usually glow brighter.
Change the layout and the picture changes. Three things decide what you see in the dark:
- Tube size. A bigger tube gives a bigger patch of light, which is easier to pick out at a glance.
- Number of tubes. More tubes means the same amount of tritium is spread more thinly, so each one gets less.
- Colour. Green looks brightest to the human eye. A green T25 can look brighter than an ice blue T100.
So the rating tells you how much tritium is in the watch. It won't tell you how bright any single marker will be. See how tritium brightness is measured for the numbers behind it.
The fairest comparison we can show is one case at both ratings. The Hawk Highland carries T25 tritium and the Hawk Nightfall carries T100. These are product photos, not a controlled test. Take them as a guide to how each rating looks.
Hawk Highland, T25 tritium
Hawk Nightfall, T100 tritium
Which NITE watches are T25 and which are T100?
If you're weighing up T25 vs T100 tritium watches to buy, here's where each rating sits across our range.
| Model | Tritium rating | Notes |
|---|---|---|
| MX10 | T25 on every colourway | Field watch, selected by UK Special Forces |
| Hawk | T25 on every colourway except Hawk Nightfall | All-terrain watch |
| Alpha | T100 | Dive watch |
| Alpha Z | T100 | Dive watch |
Our T100 tritium watches aren't all divers. The Hawk Nightfall puts T100 tritium tubes in our all-terrain case.
T25 vs T100 tritium watch: which is better?
The straight answer is… it depends on how you use the watch.
Some people prefer T25. Some people prefer T100.
The T25 watches offer a more subtle glow. That matters if you are trying to keep covert at night, and it is one of the reasons our field watch, the MX10, is T25 rated.
The MX10 Forest in the dark, a T25 tritium field watch
Meanwhile, the T100 watches offer maximum visibility in the dark, which is ideal if you depend on checking the time at a glance. Our dive watch, the Alpha series, is all T100 rated.
Pick by the job.
- Stalking at first light, or night work where you'd rather not be noticed. A soft glow is enough to read the time and won't light up your wrist. T25 fits, so an MX10 or a T25 Hawk such as the Hawk Highland.
- Diving. Light fades quickly with depth, and your dive time has to read in one glance. T100 fits, which is why the Alpha and Alpha Z carry it.
- Night navigation. Crossing Dartmoor on a night nav exercise, you want the quickest read you can get in full darkness. T100 gives you more glow to work with. The Hawk Nightfall brings that to our all-terrain watch.
The Alpha Z Explorer, a T100 tritium dive watch
Beyond the T rating, the guide to the best tritium watches for night visibility covers what else to look for.
Email theteam@nitewatches.com or call 01202 487757 with any other questions about T25 vs T100 tritium watch illumination.
You can also check out our collection of watches to see which illumination options you prefer, or use the Watch Finder to narrow it down.
Frequently Asked Questions
Is T100 brighter than T25? Usually, if the tube layout is the same, because each tube holds more tritium. Tube size, tube count and colour also change what you see, so a T100 watch isn't automatically the brighter one.
Which tritium colour is brightest? Green. Taking green as 100%, white comes in at about 60%, orange at 50% and ice blue at 40%. Each one is covered in the tritium colour guide.
How long does the glow last? Up to 20 years for both. They use the same kind of tubes, so a T25 and a T100 fade at the same rate. Year by year, it's all in the tritium lifespan guide.
Is T100 safe to wear? Yes. The tritium is sealed inside glass tubes, and the electrons it gives off can't get through your skin. See the tritium safety guide for the detail.
Are T25 and T100 legal in the UK? Yes, both. Outside Europe, some countries cap how much tritium a watch can carry without a licence. Check before you travel with a T100. Our guide to tritium watch law in the UK and Europe covers it.
Is tritium banned in watches? No. Radium dial paint went out of use decades ago, and tritium paint followed. Sealed tubes are a different technology, and that's what every NITE watch uses. Radium to Tritium covers how watches got here.
Which rating do military users prefer? It depends on the job. UK Special Forces selected the MX10, a T25 watch. A low glow suits covert work where you don't want to give away your position.
Which NITE tritium watch should I buy? For field and everyday wear, the MX10 or a T25 Hawk, or the Hawk Nightfall if you want T100. For diving, the Alpha or Alpha Z.
