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