Brightness alteration

Brightness alteration is a shift in perceived luminance in which surfaces, light sources, and the visual field as a whole appear markedly brighter or dimmer than they are.

As a drug effect it is acute and dose-proportional, resolving as the substance wears off. It ranges from a mild, pleasant intensification of colour and light to a stark, almost overwhelming glare that makes ordinary environments difficult to look at.

Brightness alteration is a common visual effect reported across a wide range of psychoactive substances. It is most commonly induced at moderate to high doses under psychedelics such as LSD, psilocybin mushrooms, and 25B-NBOH, and under stimulants such as amphetamine and methamphetamine. It also appears under cannabinoids such as cannabis, and in a more irregular, less predictable form under deliriants such as diphenhydramine and datura.

Brightness alteration is felt as an uninstructed shift in how much light the world seems to emit: whites become incandescent, shadows deepen, and colours take on a luminous quality that feels different in kind from ordinary vision. Peripheral light sources may seem to bloom or pulse faintly.

The effect is often noticed in a sudden jolt — glancing at a lit window or screen brings a fresh, startling awareness of it. At higher doses, particularly under psychedelics, the intensification can become disorienting, as though every surface has acquired its own internal light source.

Brightness alteration arises through different pathways depending on the drug class:

• Psychedelics — act on 5-HT2A receptors, amplifying cortical gain in visual processing areas and heightening the brain's response to incoming luminance signals.
• Stimulants — increase catecholamine signalling and dilate the pupils, raising the sensitivity of visual pathways to ambient light.
• Cannabinoids — act on CB1 receptors in visual cortex, altering how brightness is encoded and perceived.
• Deliriants — block muscarinic acetylcholine receptors, producing pupil dilation and a dysregulated response to light.

How much each pathway contributes in a given case is not fully understood.

Who experiences it, and how strongly, varies widely. Dose is the primary driver — low doses tend to produce a subtle brightening that many find pleasant, while higher doses can make ordinary indoor light feel harsh or overwhelming. Bright, visually busy environments intensify it, especially under psychedelics and stimulants.

People already sensitive to light report stronger shifts. Prior experience with a substance tends to calibrate expectations; simply dimming the surroundings is one of the most reliable ways to reduce its intensity.