Watch lume explained: LumiBrite, Super-LumiNova and how to charge it

How photoluminescent lume works

Modern lume pigments are based on strontium aluminate. When light hits them, electrons are pushed into a higher-energy state and trapped. In the dark they slowly fall back and release that energy as visible light. That is why lume looks brilliant just after you turn off a light and then settles into a softer glow that lasts much longer.

Nothing is used up. Lume can be charged and discharged endlessly, although the pigment can slowly degrade over many years, and the binder holding it can yellow. Older watches used radium, which glowed by itself from radioactivity and is no longer used, and later tritium paint, which faded as the tritium decayed.

Super-LumiNova, LumiBrite and tritium compared

Super-LumiNova comes in several grades and colors. The most common colors are a green tint (often called C3) and a blue tint (often called BGW9). Green lume generally looks brighter to the eye; blue-white looks cleaner on a white dial in daylight. Seiko's LumiBrite is its own photoluminescent material and is known for strong glow on Prospex divers.

Tritium tubes are tiny sealed glass vials coated inside with phosphor. They glow constantly without any charging but at a lower brightness, and they dim over the years as tritium decays, with a half-life of about 12 years.

Why some watches glow all night and others fade in an hour

• Amount of pigment: thick lume on big dive hands and markers holds more charge than a thin line on a dress watch. This is the biggest factor.
• Surface area: wide markers and broad hands simply have more glowing material.
• Color: green formulas usually look brighter to the human eye than blue or vintage-tinted formulas.
• Charge: a quick glance under a dim lamp gives a weak charge; direct sun or a UV light gives a strong one.
• Purpose: ISO 6425 dive watches must be readable at 25 cm in darkness, so their makers apply lume generously. Dress watches often use lume as a small accent or none at all.

Note.Lume claims in listings rarely include hours of glow, and conditions vary widely, so treat any comparison as general guidance.

How to charge watch lume

1. 1

   Use the strongest light you have. Direct sunlight works best. A bright LED flashlight or a UV flashlight also works well.

2. 2

   Hold the dial facing the light for 10 to 30 seconds. Lume charges quickly; longer exposure adds little.

3. 3

   Charge just before you need it, since the brightest glow is in the first minutes.

4. 4

   If you rely on lume for diving, charge it again at the surface between dives.

Note.Do not stare into a UV light. Point it at the dial only.

Lume on popular watches

Seiko 5 Sports SRPD models list LumiBrite hands and markers, and Prospex divers use LumiBrite more generously, which is one reason they are popular for night readability. See our Seiko dive watch guide. Hamilton's Khaki Field models list Super-LumiNova on the dial, which suits a field watch meant to be read at night; see best field watches.

The Tissot PRX uses lume on its hands and markers, but the slim markers on a dressy integrated-bracelet watch hold less pigment than a diver's. If strong lume is a priority, choose a dive watch with big markers. Read what makes a real dive watch to see how lume fits into diver certification.

Caring for lume

Lume needs no maintenance, but it can be damaged. Harsh chemicals and some ultrasonic cleaning can loosen lume on hands, so leave dial and hand work to a watchmaker. If lume starts to flake off a hand inside the case, have it serviced promptly, because loose particles can get into the movement. Relume work is possible on many watches but changes originality on vintage pieces.

Frequently asked questions

Which dive watches have the best lume? Watches with thick, wide lume on hands, markers and the bezel pip glow longest. Seiko Prospex divers with LumiBrite are a common example. Compare models in our dive watch guides.

Is LumiBrite better than Super-LumiNova? Both are modern photoluminescent pigments. How much is applied and its color usually matter more than the brand name.

Is watch lume radioactive? Modern Super-LumiNova and LumiBrite are not radioactive. Tritium tubes contain a small, sealed amount of radioactive gas; vintage radium dials are radioactive and should not be opened.

Why is my lume weak? Most often it was not charged strongly. Try direct sunlight or a bright flashlight for 20 seconds. If it is still weak, the watch may simply use a thin lume layer.