I haven’t done a runtime test since a while, since I was working hard on the Flashlight Review Database. Today I publish runtimes for my Zebralight - H503c - 1xAA - Samsung LH351D - 4000K - 90+ CRI headlamp.
This is my only 1x AA headlamp, so I will compare it with my Zebralight - SC5w Mk II for which I never published all the numbers. It’s a two in one runtime test today ! 
All tests were conducted in a rudimentary amateur setup, utilizing a shoebox, a cellphone and Zak Wilson’s Ceiling bounce app. I used an array of lights to calibrate the shoe box. I am very happy with the results and get consistent results with other top reviewers. Still, don’t take these numbers as the absolute truth.
Let’s start with the H503c. I bought the light in January 2022 directly from zebralight•com
Here’s the actual version I bought (full screen here):
All tests were done using Eneloop Pro 2500mAh batteries.
There is no PID with this light per ZL website description, still I tested Level 12 and 11 with and without cooling to see if there would be any difference.
Let’s start with Level 12 (Full screen here):
- Cooled runtime: The light started at 246 lumens and then dropped to 235 lumens after 30 seconds. This level is not constant, and the decrease continued gradually for more than an hour.
- Uncooled: I used another battery for this one. Still an Eneloop Pro, but I’m curious as to why the initial numbers are slightly lower and the output declines more rapidly after 68 minutes. Initially, the light emitted 233 lumens, then hit 223 lumens after 30 seconds.
Level 11 (Full screen here):
- Cooled runtime: The light started at 212 lumens, then dropped gradually for more than an hour.
- Uncooled: The light started at 208 lumens, then dropped gradually for more than an hour.
Level 8, 9 and 10 (Full screen here):
- Level 10: This is the first constant level for this light. 170 lumens for 10 minutes, then 166 lumens until the 34th min mark, then 162 lumens until the major drop after 103 minutes.
- Level 9: 108 lumens flat for 199 minutes.
- Level 8: 60 lumens flat for 392 minutes.
SC5w MK II
Before comparing the H503c, let’s have a quick look at the SC5w MK II. I will start to compare at level 10 and 11.
Here’s the actual version I bought in January 2022 (full screen here):
Level 12 (Full screen here):
- Cooled runtime: The light started at 475 lumens for 1.5 min, then dropped to 465 lumens for an extra 1.5 min then dropped to 313~319 lumens until the 52nd min.
- Uncooled: The light started at 475 lumens, but quickly dropped to 426 lumens until the 3rd min mark, then stayed at 321 lumens for a total of 37 min before the major drop.
Level 10-11 (Full screen here):
- This is where it’s getting interresting. The SC5w level 10 is the closest to H503c level 12, but shows much more efficacy. The SC5w is holding 213-217 lumens for 91 minutes.
- SC5w level 11 performances are also impressive as it hits a 291-304 lumens range for almost 60 minutes.
Level 8-9 (Full screen here):
- Both lights are showing similar performances at Level 8 and 9. For level 9, the SC5w stayed at 121 lumens for 187 min. For level 8, the SC5w had a steady 61 lumens for 379 min.
Cheers !