Does light actually affect our mood?
It does. How much light there is, when it arrives and its colour change how alert you feel. That is not a slogan. The effect has been measured.
What is being measured?
The International Commission on Illumination writes that light does more than let you see. Alertness, body clock and sleep are affected too. The measure is light at the eye. It uses a weighting more sensitive to shorter wavelengths, the light closer to blue. The name is melanopic EDI.
The 2022 text by Brown and colleagues gives three numbers for healthy adults. At least 250 at the eye in the day. At most 10 in the three hours before bed. Near 1 during sleep. Plenty in the day, low in the evening, near darkness at night.
Light that still looks like noon in the evening keeps the room in daytime.
Why does the usual light at home sit apart?
In most homes one source paints every surface the same. Light arrives from above, reaches the eye, and the colour looks like day. That is right for walking and seeing clearly.
If that setting stays into the evening, the numbers sit above the evening threshold. The body still reads the day as going on. The fault is not the model of the ceiling. The fault is carrying light that still looks like noon into the night.
What does another light change?
Light spread on a wall, lower and warmer, loads the eye less. A light close to sunset and a light that still looks like noon are not the same job. This is not a race in lumens. It is how the light reaches you.
That has a name in what is ambiance?. The layer is in light in a room is not a single layer.
Is this a treatment?
It is not. The CIE and Brown texts give a general pattern for healthy adults. They do not turn a home lamp into a medical device. There is no claim for sleep disorders or seasonal low mood.
The job at home is this: do not carry light that looks like day into the night.