The Deep Blue DayNight Diver PC is a 44mm-class automatic dive watch with T100 tritium illumination, a sapphire crystal, 200-meter water resistance and a lightweight polycarbonate case. I bought it as my first automatic watch after years of preferring quartz, and the watch has turned out to be an interesting change of pace. The blue-and-yellow tritium was the biggest question mark for me, but in actual use I found the DayNight remarkably easy to read in darkness, including the seconds hand.
Deep Blue DayNight Diver PC Specifications
| Specification | DayNight Diver PC |
|---|---|
| Model | DNPCAUTOWHITEBLUE |
| Case material | Polycarbonate |
| Case diameter | 44 mm listed in specifications |
| Case thickness | 14 mm |
| Lug-to-lug | 51 mm |
| Lug width | 22 mm |
| Movement | Seiko NH35 automatic |
| Crystal | Sapphire |
| Water resistance | 200 m / 660 ft |
| Bezel | Unidirectional, 60-click |
| Tritium | T100-capacity GTLS |
| Tritium tubes | 17 |
| Dial | Black/white |
| Hands | Yellow tritium |
| Strap | Tritium-integrated rubber |
| Date | Yes |
| Weight | Under 100 g according to the article |
| Battery | Not applicable; automatic movement |
The source specification table identifies the watch as the DayNight Diver PC DNPCAUTOWHITEBLUE, with a 44 mm case, 14 mm thickness, 51 mm lug-to-lug, 22 mm lugs, NH35 movement, sapphire crystal and 200-meter water resistance. It lists 17 tritium tubes with T100 capacity.
The article also describes the case elsewhere as 45 mm, so I would treat the diameter as approximately 44–45 mm rather than trying to resolve the discrepancy without checking the manufacturer’s current specification.
Our Experience With the DayNight Diver PC
This watch represented something of a departure for me because it was my first automatic watch.
I have traditionally preferred quartz movements. I like their accuracy, convenience and low-maintenance nature, so buying an automatic was partly an experiment to see whether I would enjoy the mechanical side of watch ownership.
I did.
The first thing I noticed was the difference in the way the seconds hand moves. Compared with my quartz watches, the sweeping motion of the NH35 gives the watch a different character. It feels more mechanical and alive on the wrist, which is something I hadn’t really experienced with my predominantly quartz collection.
The other surprise was the weight. I expected a polycarbonate watch to feel extremely light, but the DayNight has enough physical presence that it feels substantial. The combination of the large case and automatic movement probably contributes to that impression.
That hasn’t been a negative for me. It simply means that “polycarbonate” shouldn’t be interpreted as meaning that this is an almost weightless watch.
The Polycarbonate Case
The DayNight Diver PC uses a lightweight polycarbonate case.
The source describes the case as 44 mm in diameter, 14 mm thick and 51 mm lug-to-lug. Elsewhere, the article describes the case as 45 mm, so there is a one-millimeter discrepancy in the source material.
Regardless of which published dimension is used, this is a large watch.
The 51 mm lug-to-lug measurement is particularly relevant because it tells us more about wrist presence than diameter alone. The integrated strap arrangement and curvature of the case help keep that length from feeling excessive on my wrist.
I found the watch comfortable enough for extended wear, and the polycarbonate construction avoids the weight associated with a similarly sized stainless-steel diver.
That is one of the most compelling aspects of this particular DayNight model. It gives you the visual presence of a large dive watch without making the wrist carry the mass of a large steel case.
The Sapphire Crystal
The DayNight Diver PC uses a sapphire crystal.
That was one of the specifications I particularly wanted to see on a tritium dive watch. Sapphire is highly resistant to scratching, making it a sensible choice for a watch intended to be used rather than simply displayed.
I also found the crystal exceptionally clear when I first received the watch. The dial markings were easy to see, and the clarity of the crystal contributed to the overall legibility.
The raised bezel provides some additional protection around the crystal. I liked that feature because the bezel sits slightly above the crystal, reducing the likelihood that the crystal will be the first point of contact if the watch encounters something.
The DayNight Dial
The black-and-white dial is straightforward and highly legible.
Large Arabic numerals provide the primary hour indications, while smaller 24-hour markings add a second time scale without making the dial excessively complicated. The date window sits at 3 o’clock.
One small detail I particularly like is the black-on-white date display.
The source notes that the date window uses black numerals on a white background rather than the white-on-black arrangement found on some watches. That doesn’t bother me at all, and I actually find it easier to read because of my farsightedness.
The dial is therefore functional first. It isn’t trying to be a dress watch or a minimalist watch, but the layout works very well for its intended purpose.
T100 Tritium: The Real Reason to Own It
The illumination is the feature that makes the DayNight Diver PC particularly interesting.
The watch uses 17 tritium gas tubes, with two yellow tubes at 12 o’clock and blue tubes at the other hour positions. The hour, minute and seconds hands also use yellow tritium. The specification describes the system as having T100 capacity.
That gives the watch a very distinctive appearance in darkness.
I initially wondered whether the blue tubes would actually work well. Green is generally easier for the human eye to see in darkness, so I wasn’t sure whether the blue markers would provide enough contrast to make the watch genuinely useful at night.
My concern turned out to be misplaced.
In complete darkness, the DayNight is extremely easy to read. The blue markers are clearly visible, the yellow hands stand out against them, and I can even see the seconds hand. That is significant because seconds-hand visibility is not something I take for granted on a tritium watch.
I consider the DayNight one of the most readable watches in my collection, alongside my other Deep Blue DayNight Solar.
The Blue and Yellow Combination
The colour combination is more than a cosmetic feature.
The blue hour markers and yellow hands create useful separation between the different components of the dial in darkness. Instead of producing a single mass of glowing material, the illumination preserves the basic structure of the dial.
That is particularly helpful when reading the time quickly.
The yellow tube at 12 o’clock also gives you an immediate orientation point. The bezel has a yellow tritium tube at 12 o’clock as well, extending the same basic colour-coding into the dive-timing system.
I originally worried that the blue would be difficult to see. In actual use, it became one of the most distinctive features of the watch.
The Seiko NH35 Automatic Movement
The DayNight uses a Seiko NH35 automatic movement.
For me, this was a significant part of the ownership experience because it was my first automatic watch. I have generally favoured quartz, so experiencing the sweeping seconds hand was one of the reasons I enjoyed wearing the DayNight.
The source describes the NH35 as having 24 jewels, approximately 41 hours of power reserve, hacking seconds and hand-winding capability. It also reports real-world accuracy of approximately +15/-10 seconds per day from the example tested.
Those characteristics make the NH35 a very practical automatic movement for this type of watch.
There is, however, a trade-off compared with quartz. An automatic watch can stop if it is not worn or wound sufficiently, whereas a quartz watch can sit for months and remain ready to use. That difference is something I notice because of my longstanding preference for quartz.
The Sweeping Seconds Hand
The sweeping seconds hand is one of the small pleasures of the watch.
After years of mostly wearing quartz watches, I immediately noticed the difference. The seconds hand moves continuously around the dial rather than making the distinct one-second jumps associated with a typical quartz movement.
This doesn’t make the watch inherently more accurate or more useful, but it changes the character of the ownership experience.
For me, that was one of the reasons buying the DayNight as my first automatic turned out to be worthwhile.
The 60-Click Bezel
The DayNight uses a unidirectional 60-click rotating bezel.
I find the bezel action good, although I don’t personally use watch bezels very often. If I need a timer, I generally reach for a Casio, which is one reason I have never been particularly interested in analog chronographs either.
The bezel is still an appropriate feature on the watch because it reinforces its dive-watch purpose. The unidirectional design is conventional for a dive timer, and the yellow tritium tube at 12 provides a visible reference point in darkness.
The 60-click configuration is also worth noting because the number of bezel clicks affects how precisely the bezel can be aligned for timing.
200-Meter Water Resistance
The DayNight Diver PC is rated to 200 meters, or 660 feet.
That provides substantial capability for recreational diving and considerably more water resistance than most everyday watches require. The original article describes the case as relying on its polycarbonate construction and O-ring seals for water resistance.
The crown specification in the source is listed as push-in, rather than screw-down. Because the article contains some conflicting terminology elsewhere, I would verify the current manufacturer’s crown specification before making a stronger claim about the crown construction.
The 200-meter rating itself is clearly stated in the specifications.
The Rubber Strap
The supplied rubber strap is another feature I like.
It is relatively thick and feels durable rather than flimsy. The strap also incorporates tritium tubes, extending the watch’s nighttime illumination beyond the dial and bezel.
The strap is 22 mm wide, giving the watch a standard lug-width dimension for anyone interested in experimenting with alternatives.
The integrated appearance works particularly well with the polycarbonate case. It keeps the watch looking like a single purpose-built instrument rather than a conventional watch with a generic aftermarket strap.
Wearing the DayNight Diver PC
The watch is large, but I don’t find it awkward on my wrist.
The 51 mm lug-to-lug measurement sounds substantial, but the case curvature and integrated strap design help the watch follow the wrist rather than simply sitting across it. The original review notes that it wears smaller than its specifications might suggest, and my own experience is consistent with that observation.
I also appreciate the relatively low weight.
The specification doesn’t provide an exact measured weight, but describes the watch as being under 100 grams because of the polycarbonate case.
That combination—large dimensions without the corresponding weight—is one of the strongest practical arguments for the DayNight Diver PC.
What I Like About the Deep Blue DayNight Diver PC
The T100 illumination is the obvious highlight. I was initially skeptical about the blue tritium, but the watch proved exceptionally readable in darkness. Being able to see the seconds hand is an especially useful characteristic for me.
I also like the polycarbonate case. It gives the watch a large, substantial appearance while keeping the weight down.
The sapphire crystal is another major positive. Combined with the raised bezel, it gives me confidence that the dial has a good degree of protection from everyday scratches and knocks.
The NH35 automatic movement has also made the watch more interesting to me because it was my first automatic. The sweeping seconds hand gives the watch a different character from the quartz watches that make up most of my collection.
Finally, I like the overall legibility. The large markers, high-contrast dial and differentiated tritium colours make this one of the easiest watches in my collection to read.
What I Don’t Like
The biggest drawback for me is not actually a functional problem. It is simply that the watch is large and relatively tall.
At approximately 44–45 mm across and 14 mm thick, it has a substantial presence. Someone who prefers compact watches will probably find it too large regardless of how light the polycarbonate case makes it.
The automatic movement is also both an attraction and a limitation for me. I enjoyed having my first automatic, but I still prefer quartz for its simplicity and grab-and-go convenience.
The 60-click bezel isn’t an issue, but I personally don’t make much use of mechanical bezels. That’s simply a reflection of how I use watches rather than a criticism of the watch itself.
DayNight Diver PC vs. Quartz Tritium Watches
The DayNight Diver PC occupies an interesting position in my collection because most of my other watches use quartz.
A quartz tritium watch is generally the simpler tool. It can sit unused for long periods and remain ready to go, and the movement doesn’t require the owner to think about power reserve.
The DayNight adds mechanical character at the cost of some convenience.
The NH35 gives me the sweeping seconds hand and the experience of wearing an automatic movement, but the watch needs to be worn or wound to keep running. For someone who enjoys mechanical watches, that’s part of the appeal. For someone who prioritizes pure convenience, quartz remains the more practical choice.
Having now owned an automatic, I understand the attraction much better than I did before buying this watch.
DayNight Diver PC vs. NITE Alpha Crest
The NITE Alpha Crest is a particularly useful comparison because both watches are substantial tritium dive watches with sapphire crystals and serious water resistance.
The Alpha Crest uses T100 tritium and a 42 mm stainless-steel case, while the DayNight uses a larger polycarbonate case and an NH35 automatic movement. The DayNight also uses a distinctive combination of blue and yellow tritium, while the Alpha Crest relies heavily on blue T100 markers.
For me, the difference is partly about what I want from the watch.
The Alpha Crest gives me the heavier, more conventional stainless-steel dive-watch experience with T100 illumination. The DayNight gives me a lighter case and the mechanical character of an automatic movement.
Both are interesting precisely because they approach the tritium dive-watch concept differently.
Is the Deep Blue DayNight Diver PC a Good Tritium Watch?
Based on my experience, yes, particularly if nighttime legibility is a priority.
The unusual colour combination initially made me skeptical. I expected the blue tubes to be less visible than conventional green tritium, but that isn’t what I experienced. The blue markers are clearly visible, the yellow hands provide excellent contrast, and the seconds hand remains readable in darkness.
The watch also gets the other major tritium-watch fundamentals right: sapphire crystal, a substantial water-resistance rating, continuous GTLS illumination and a practical case design.
The automatic movement adds another dimension that isn’t present on many tritium watches. For someone who normally wears quartz, the NH35 makes the DayNight a more interesting ownership experience.
Who Is the DayNight Diver PC For?
The watch is particularly well suited to someone who wants a large, lightweight automatic watch with strong T100 tritium illumination.
It should also appeal to buyers who like the idea of a mechanical movement but don’t want to carry the weight of a similarly sized stainless-steel diver.
It is less suitable for someone who wants a small or thin watch, or someone who prioritizes quartz convenience above mechanical character.
For me, the DayNight occupies an unusual but useful place in the collection. It gives me an automatic movement I enjoy wearing while retaining the tritium visibility that originally attracted me to the watch.
Our Final Thoughts
The Deep Blue DayNight Diver PC turned out to be a particularly interesting addition to my collection.
I bought it as my first automatic watch, which already made it something of an experiment for me because I have traditionally preferred quartz. The NH35 changed my opinion somewhat. I enjoy the sweeping seconds hand and the mechanical character it gives the watch.
But the reason this watch really stands out on TritiumLume is its illumination.
I wasn’t sure the blue tritium would work as well as conventional green illumination, particularly because blue is generally less visible to the human eye in darkness. In actual use, however, I found the DayNight remarkably easy to read. The blue hour markers and yellow hands provide enough differentiation that I can read the time quickly, and I can even see the seconds hand.
The combination of T100 tritium, sapphire crystal, 200-meter water resistance, polycarbonate construction and an NH35 automatic movement makes this a distinctive watch rather than simply another tritium diver.
It is large and relatively tall, and the automatic movement sacrifices some of the grab-and-go simplicity I like about quartz. For me, though, those compromises are balanced by the excellent nighttime legibility and the novelty of owning and wearing my first automatic.
The DayNight Diver PC has earned its place in my collection, and it remains one of my most readable watches in darkness.
Anonymous-
I have the all green on a grey strap. I wear it more than any other, though I wish it was quartz. I prefer a 60 clicker they seem more positive or something.