Top 20 Rankings
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.
|1||Axios Iron Clad||17|
|2||Zelos Horizons 43||16|
|4||Zelos Mako 3 Ti||15|
|6||Zelos Horizons 39||13|
|7||SWC Diver mk 2||12|
|11||Squale Corso Italiano Artico||10|
|14||Aragon Divemaster 4||9|
|17||RLG Odyssea 4||8|
|17||DIY Watch Club Sandwich Dial||8|
|17||Seiko 5 SRPG35||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.
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.
- 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