J-Scores
Top 20 Rankings
UPDATED 2/17/2022
Note that J-Score is not a rigorously scientific measurement. If I measure the same watch multiple times I will usually get slightly different results.
| Rank | Watch | J-Score |
| 1 | Axios Iron Clad | 17 |
| 2 | Zelos Horizons 43 | 16 |
| 2 | Namica Shirahama | 16 |
| 4 | Zelos Mako 3 Ti | 15 |
| 5 | Orient Ra-0ACK | 14 |
| 6 | Zelos Horizons 39 | 13 |
| 7 | SWC Diver mk 2 | 12 |
| 7 | Boldr Odyssey | 12 |
| 7 | SWC Ark | 12 |
| 10 | Zelos Spearfish | 11 |
| 11 | Seiko Samurai | 10 |
| 11 | Revelot Hexmariner | 10 |
| 11 | Squale Corso Italiano Artico | 10 |
| 14 | Alba AQPJ403 | 9 |
| 14 | Aragon Divemaster 4 | 9 |
| 14 | Steeldive SD1970 | 9 |
| 17 | RLG Odyssea 4 | 8 |
| 17 | DIY Watch Club Sandwich Dial | 8 |
| 17 | Seiko 5 SRPG35 | 8 |
| 17 | Seiko Speedtimer | 8 |
What is J-Score?
J-score is an attempt at creating an objective score of the apparent brightness of the lume on a watch one hour after it has been fully charged with a UV light. It is measured by taking a photo of the watch after one hour, and measuring the RGB values of pixels on the hands and markers.
J-Score is not scientifically rigorous, and yields slightly different results each time I test. But in my opinion it gives a pretty good comparison of lume across different watches.
Testing Procedures
Below is the testing equipment and procedures I use. I'm sure there's some errors in there, and probably a better way of crunching the numbers.
Camera Equipment and Exposure
- Panasonic Lumix G85 with a Lumix G 1:1.7/20 Lens
- 3840 x 2160 (4K) Resolution
- 4 second Exposure, ISO 400, F 4.5
- Camera on tripod extended horizontally over the watch, such the viewfinder covers 10cm of vertical space. I measure this by marking out a 10cm square on a piece of paper and adjusting the height of the camera until it fits perfectly in the vertical edges of the viewfinder.
Testing procedure
- In a completely dark room, charge the watch for 10 seconds using a UV flashlight.
- After one hour in darkness take a picture of the watch using the exposure settings above (I usually just se the camera to do a time lapse)
- Open the photo in Photoshop (or any image editor)
- Use the eyedropper tool to measure the RGB values of three representative points on the hands, and three on the markers. Record these values.
- Convert each recorded value into a measurement of apparent luminosity using this formula: R0.21+G0.72+B0.07
- Average the resulting luminosity values for the hands and then average the markers. This will give you a raw luminosity score for the brightness of the hands and markers after 1-hour in the dark
- Using the above procedures, calculate the Raw luminosity of a Seiko Samurai's hands and markers (on my equipment that's 30.7 for the markers and 32.6 for the hands)
- Divide the raw luminosity scores of the watch you're measuring by corresponding scores of the Seiko Samurail, and multiply by 10. This will give you two J-scores, one for the hands, one for the markers.
- Average the J-scores of the hands and markers to get the total J-score