Why do transition lenses go dark in sunlight when you’re outside but not when you’re in a brightly lit room?

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Why do transition lenses go dark in sunlight when you’re outside but not when you’re in a brightly lit room?

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12 Answers

Anonymous 0 Comments

First, a “brightly” lit room is FAR dimmer than direct sunlight. A typical brightly-lit indoor space is at an illumination of about 500 [lux](https://en.wikipedia.org/wiki/Lux). The direct light in a TV studio is perhaps 1,000 lux. Direct sunlight goes as high as *100,000* lux at noon in the tropics.

But it turns out the relevant part here is ultraviolet light. The sun is reasonably bright in near-UV, but indoor lighting is not, and it’s UV that triggers the lenses to darken.

Anonymous 0 Comments

The brightness of an indoor room is minuscule compared to direct sunlight.

* 32,000–100,000 Lux Direct sunlight
* 1,000 lux overcast day, TV studio (bright lit)
* 300-500 lux office
* 100 – 150 lux typical living room

Your vision system is adaptive so you do not notice the huge difference in illumination indoors compared to outdoors.

Anonymous 0 Comments

UV rays activate. Which means they’re useless in a car because your windshield has some uV protection.

Anonymous 0 Comments

Your eyes do not have a linear sense of brightness. In other words, a room that seems twice as bright to you is not actually twice as bright.

Instead, your eyes/brain have a logarithmic sense of brightness. In near-darkness, we can detect even very small changes in brightness. A candle flame might seem twice as bright as a smaller candle next to it, but not be actually twice as bright by scientific measurement.

But in bright light, our eyes cannot detect small changes in brightness anymore. For example, a brightly lit sunny day can be literally 2,000 times brighter than a very brightly lit room, but does not feel that way to our eyes.

But you better believe a pair of transition lenses can tell the difference.

Anonymous 0 Comments

First, a “brightly” lit room is FAR dimmer than direct sunlight. A typical brightly-lit indoor space is at an illumination of about 500 [lux](https://en.wikipedia.org/wiki/Lux). The direct light in a TV studio is perhaps 1,000 lux. Direct sunlight goes as high as *100,000* lux at noon in the tropics.

But it turns out the relevant part here is ultraviolet light. The sun is reasonably bright in near-UV, but indoor lighting is not, and it’s UV that triggers the lenses to darken.

Anonymous 0 Comments

Your eyes do not have a linear sense of brightness. In other words, a room that seems twice as bright to you is not actually twice as bright.

Instead, your eyes/brain have a logarithmic sense of brightness. In near-darkness, we can detect even very small changes in brightness. A candle flame might seem twice as bright as a smaller candle next to it, but not be actually twice as bright by scientific measurement.

But in bright light, our eyes cannot detect small changes in brightness anymore. For example, a brightly lit sunny day can be literally 2,000 times brighter than a very brightly lit room, but does not feel that way to our eyes.

But you better believe a pair of transition lenses can tell the difference.

Anonymous 0 Comments

The brightness of an indoor room is minuscule compared to direct sunlight.

* 32,000–100,000 Lux Direct sunlight
* 1,000 lux overcast day, TV studio (bright lit)
* 300-500 lux office
* 100 – 150 lux typical living room

Your vision system is adaptive so you do not notice the huge difference in illumination indoors compared to outdoors.

Anonymous 0 Comments

UV rays activate. Which means they’re useless in a car because your windshield has some uV protection.

Anonymous 0 Comments

The lenses react to ultraviolet light (light that we can’t see but is still there; it’s the light that causes sunburn).

A bright room is probably a result of bulbs emitting mostly yellow light. This is the wrong frequency for the lens to react to, so it doesn’t. Even a white bulb (a mixture of frequencies) is emitting mostly visible light and not wasting energy by producing light we can’t see.

Anonymous 0 Comments

The lenses react to ultraviolet light (light that we can’t see but is still there; it’s the light that causes sunburn).

A bright room is probably a result of bulbs emitting mostly yellow light. This is the wrong frequency for the lens to react to, so it doesn’t. Even a white bulb (a mixture of frequencies) is emitting mostly visible light and not wasting energy by producing light we can’t see.