How Your Eyes Adjust to the Dark | How Long Dark and Light Adaptation Take

Dark adaptation and light adaptation take very different times

Adaptation is the eye changing its sensitivity to match the brightness around it. Adjusting toward darkness is dark adaptation; adjusting toward brightness is light adaptation. Both are “getting used to it”, but the time they take is completely different.

Slow dark adaptation and fast light adaptation may seem lopsided, but it matches experience. Stepping out onto a dark street at night, you wait for things to “come into view”, whereas the glare when you leave a tunnel settles within a few blinks.

Why it takes time: the roles of two kinds of photoreceptors

The retina at the back of the eye has two kinds of cells that receive light. They cover different ranges of brightness, and that difference produces the time gap in adaptation.

In bright places the cones do most of the work, and you see both color and detail. When it gets dark the cones can no longer work and the rods take over. That handover takes time, and it is the essence of dark adaptation. The light-sensitive pigment in rods (rhodopsin) is broken down by light in bright conditions, and sensitivity doesn’t return until it has been rebuilt in the dark.

If you plot dark adaptation on a graph, cone sensitivity rises over the first few minutes and levels off, then rod sensitivity catches up and climbs much further: a two-stage curve. That is why, after you begin to see a little, there comes a moment when you suddenly see more.

Light adaptation, on the other hand, is a change toward lower sensitivity. It only has to calm down an over-responding system, so it is much quicker than dark adaptation, which has to rebuild sensitivity.

Why you can’t see colors in the dark

Try picking clothes after turning off the light at night and you can tell their shapes but not their colors. Only the cones handle color, and the rods working in the dark can’t tell colors apart. In the dark, you see the world in something close to monochrome.

As it gets darker, how you perceive brightness also changes. In bright light red and orange stand out, but in dim light blue and green look relatively brighter (the Purkinje effect). When only the blue signs seem to glow at dusk, you are seeing this switchover in progress.

• In the dark, red things look darker than they really are. For displays meant to be seen at night, blue-green colors are more noticeable.
• For the same reason, red light barely stimulates the rods. Red lights are used for stargazing and darkrooms because they light up what’s in your hands while disturbing dark adaptation as little as possible.
• Looking at a phone screen in the dark undoes the dark adaptation you have built up in one go. If you want to see outside at night, looking at the screen less often helps most.

Tips for seeing a little better in the dark

You can’t speed up adaptation by willpower, but setting up the right conditions makes a noticeable difference.

1. 1

   Avoid looking at bright light

   A single look at a bright light sets dark adaptation back a long way. Looking at flashlights or phone screens less often is the most effective step. If you must, turn the brightness all the way down.

2. 2

   Don’t look straight at what you want to see; look slightly to the side

   The center of your vision (the fovea) has almost no rods. In the dark, the very point you look straight at can therefore be blurry or invisible. Looking a little to one side of your target lets you catch it with the rod-rich periphery, and you actually see it more clearly.

3. 3

   Close one eye before stepping into the light

   If you go back and forth between dark and bright places, keeping one eye closed while you are in the light preserves that eye’s dark adaptation. It is a classic technique for night work.

4. 4

   Prepare before you enter the dark

   Instead of waiting after you go in, dim the lights beforehand so the switch is gentler. On nights when you may need to get up, not making the lights too bright before bed makes it easier to move around.

How adaptation differs from afterimages

Adaptation and afterimages are close relatives in the sense that what you saw “lingers”. Both happen when photoreceptors receive the same stimulus for a while and their sensitivity becomes skewed. The difference is the area affected.

Stare at a color-inverted image for a few tens of seconds and then switch to a black-and-white version, and you will see color in it. Only the area you stared at loses sensitivity to certain colors, so the opposite colors appear to float up. In the afterimage illusion tool you can choose a staring time of 10, 20, 30 or 45 seconds; trying different times lets you feel how the skew in sensitivity grows stronger over time. For how afterimages themselves work, see how color afterimage illusions work, and if the image seems to linger on the screen itself, how to tell screen image retention from burn-in helps you tell them apart.

FAQ

How many minutes does it take for your eyes to adjust to the dark?

You can see well enough to get around within a few minutes, but adapting almost fully takes about 30 minutes. In the first few minutes the color-sensing cones become more sensitive; after that the rods, which handle dim light, catch up and you see even more, a two-stage change. Light adaptation when you step into bright light is fast, settling within tens of seconds to about a minute.

Why can’t I see colors in the dark?

The photoreceptors that tell colors apart, the cones, only work in bright light. In the dark the rods, which can’t distinguish colors, take over, so you can make out shapes but not colors. Also, as it gets darker, red looks dimmer and blue and green look relatively brighter (the Purkinje effect).

Where should I look when it’s hard to see in the dark?

Shift your gaze slightly to the side of what you want to see. The center of your vision has almost no rods, which handle dim light, so the very point you look straight at can be blurry. Peripheral vision copes better with darkness, so not looking directly lets you see it more clearly. Avoiding bright light such as phone screens also preserves the dark adaptation you have built up.

Why are red lights used at night?

The rods that work in the dark barely respond to red light, so red lighting lets you see what’s in your hands without breaking dark adaptation much. It is used for stargazing, darkrooms and night-time instrument lighting. Looking at white light of the same brightness sets dark adaptation back a lot, so when you want to stay adjusted to the dark, the basic rule is to reduce both the color and the brightness.