Circadian and tunable white lighting

The premise is uncontroversial: light exposure influences when people feel alert and when they feel sleepy, and the timing and character of that light matters. Bright cool light in the morning and dim warm light in the evening broadly matches what the sun does, and following it loosely is a sensible thing to do.

Where the marketing runs ahead of the reality is scale. Outdoor daylight is enormously brighter than any indoor lighting - the gap is not a matter of a few percent but of orders of magnitude. A tunable bulb in a ceiling fitting is working with a tiny fraction of the signal that stepping outside provides.

So the honest framing is: tunable lighting at home is a nudge, not a treatment. It can make an evening feel calmer and a morning feel more alert. It is not going to substitute for daylight, and any product suggesting otherwise is overselling.

Here is the part worth emphasizing, because it costs nothing and it is where almost all of the benefit sits: the evening end of that table is the half that matters, and you do not need a tunable bulb to do it.

A 2700K bulb at CRI 95 on a dimmer gives you warm, dim evening light - which is the recommendation this site makes for living rooms and bedrooms anyway, for reasons that have nothing to do with circadian anything. If your house is already 2700K and dimmable in the evening, you have captured most of the available benefit without buying a single smart device.

The morning half is harder to deliver and less important, mostly because a bulb cannot compete with a window. Opening curtains earlier does more than any tunable bulb will, and going outside does more than both.

So the honest recommendation is: get 2700K and dimming right everywhere first. Buy tunable bulbs only for the rooms where the extra flexibility solves a real problem.

Tunable white is worth paying for in rooms that do two genuinely different jobs at different times, because there the alternative is two light fittings.

• A home office that is also a bedroom. Cool and bright for work, warm and dim afterwards, from one fitting. This is the clearest case.
• A kitchen used for cooking and for eating. Task-appropriate during preparation, warmer at the table.
• A child's room. Bright for play, very dim and warm for sleep - the two-layer problem described in kids' room lighting.
• A studio apartment. Where one room is every room, and there is no second fitting to switch to.

For those, a LIFX A19 at 1,100 lumens and 90+ CRI is the pick among tunable bulbs on this site, because it publishes a CRI figure - most do not, and a tunable bulb with poor color rendering has solved the wrong problem. A WiZ tunable bulb is the lower-cost option, and a Sengled Matter bulb is the one least likely to be stranded by an app going away.

Whichever you buy, put the transition on a schedule rather than on a decision. Anything requiring you to remember to change the lights at 8pm will not survive - the automations that last are covered in schedules and automations, and sunset-based triggers beat fixed times for exactly the reason described there.