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“Dim between turns” getting stuck at very dim

Saturday 1 April
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Hi, I finally had a chance to use the app in an area with map coverage. 

I have “dim between turns” enabled. I found that it worked as expected at first. After a few minutes of riding, the display seemed to get stuck in a “mostly dimmed” state - barely visible but not black. There was lots of ambient light - but not direct sunlight on the screen. 

I manually increased the screen brightness to 100% (it was at ~25%). That worked until the c.t app dimmed the screen again. Then the screen stayed at about 25% brightness again. 

I will try again tomorrow after restarting the phone. In the meantime I thought I would check whether anyone else observed this behavior. 

iPhone 14 Pro, iOS version up to date, battery was not low, and low power mode was not on. 

Thanks, Brad


Sun 2 Apr, 21:39

I think “aaargh” is my comment on this one. :)

Apple provides a helpful way for apps to set the phone’s brightness. This is what c.t uses to dim between turns, and then undim when there’s a turn imminent.

Unfortunately… it doesn’t always work. Basically there appears to be a bug in how the iPhone mediates between app-set brightness and user-set brightness.

c.t has a bunch of code to get round this and it works for me (I tested it again on today’s ride) but it sounds like it’s still not infallible. I’ll take another look. If you find any way to consistently trigger it that’d be great.

Out of interest – when you say “about 25%”, do you think it’s plausible it might be 15%? That might line up with something in the code.

Mon 3 Apr, 09:14

Hi Richard,

I tried it today and came to a similar conclusion - that it may be a bug in iOS itself. I could not consistently trigger it today, but in about 5 hours of riding it worked correctly around 90% of the time. At least there’s a workaround to manually adjust the brightness. 

I can believe that it’s 15% brightness. I’ll try to look more closely next time but I don’t have calipers with me 😀 

Sun 16 Apr, 01:20

Richard, after about two weeks of heavy use I have not found this issue to be common. I still can not reproduce it reliably, but I suspect it’s related to switching between different apps (e.g. camera). It does feel more like a systemwide behavior issue. Sometimes (rarely) it gets set to 0% brightness. 

Once I did catch it in the act: from the app I swiped down from the top left corner to access the Lock Screen. Long press on the camera icon. Then about a half second after the camera opened, the screen dimmed. 

Wed 30 Aug, 22:58

I’ve likewise found this to be an inconsistent problem and I’m struggling to reproduce it reliably.  I turned the auto illumination functions (E.g. night shift etc) all off on my iPhone SE and that seemed to increase the frequency of the error (to ~100%).   I’ve quite a few miles ahead of me over the next couple of weeks and will try to narrow it down.  Directions on phone/app settings to test would be useful (be great to get it working 100%, as it is a smart idea).

Thu 31 Aug, 17:00

Noticed this too (iPhone 14, display settings: auto-adjust off and true-tone off) - but infrequently and only on long rides, maybe 6h into the ride.

Fri 1 Sep, 12:45

It dimmed at every turn for me when the ambient light was low.  Is it related to the phone‘s light sensor (possibly located behind the camera lenses) and the phone being mounted on the bike stem, pointing downwards, with the lens partially obscured (on my set-up). Does the phone think it is dark and adjust appropriately by dimming the screen? I’ll check by putting the camera on selfie mode, so the light sensor is pointing upwards.  If that doesn’t work, I’ll try turning the auto-brightness off under settings, accessibility, display&text size. 

Fri 1 Sep, 15:51

That would be really interesting – let me know what you find.

As mentioned above, is just telling the iPhone “dim the screen” or “undim the screen” – nothing more than that. The issue appears to be that the iPhone sometimes thinks it knows better and it’s not quite clear what circumstances this is in!

Fri 1 Sep, 18:47

Could the c.t generate a loop, where ‘undim’ recovers to a previous screen illumination level even when that illumination level is no longer appropriate (like when you’ve cycled out of a shaded area into sunshine, and where the screen should be brighter); so it will either stay slightly dimmed or step down to a new dimmer option (rather than cross referencing to the ambient light)? I think I’ve observed it ‘stepping down’ (but difficult to say when moving between light and shade). I’ll keep you posted anyhow.  

Sat 23 Sep, 17:28

Turning the auto brightness function off as per post above worked … mostly.  Very occasionally, possibly linked to swopping to other apps and/or the phone turning to low power mode (<20%), the screen reverting to a ‘night-time’ level of illumination (consistent with others’ observations).