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