PowerSwitch

These consist of a miniature fluorescent lamp, or increasingly an LED array, a small rechargeable battery, a battery charger and a changeover circuit.

Under normal conditions the battery is kept charged from the mains. If the power fails, then the light source is illuminated from the battery for typically 3 hours.

They are fully automatic and no attention is needed.

They are not ideal for the generally well prepared members of these forums for the following reasons.
1) They cant be turned off, so a power failure at noon, during daylight, will fully discharge the battery before darkness falls and the light is needed.
2) They only run for 3 hours, or a bit longer.
3) Not portable.
4) Ongoing electricity consumption.

I would however strongly recommend these emergency lights for elderly or disabled friends or relatives.
The fully automatic operation with no user input whatsoever is a great attraction.
They should be fixed to the ceiling or high up on the wall, and permanently connected to the lighting circuit.

Unlike a torch or lantern, they cant be "tidied away" and then forgotten about.

Even a single such emergency light will be most valuable, several would be better. Locations would depend on the layout of the home. High risk places include stairs and bathrooms,
Not suitable for bedrooms.

Available from many suppliers, be sure to obtain reasonable quality items intended for use in public buildings, and NOT smaller or cheaper units intended for domestic use.
Menvier are a reputable make and widely sold on fleabay.
Replace the battery every five years.

adam2 wrote:1) They cant be turned off, so a power failure at noon, during daylight, will fully discharge the battery before darkness falls and the light is needed.

Surely a sensible addition would be a light level sensor? They’re built into every cheap and nasty solar garden light (and my car has several, phones have them too) so it can’t be difficult.

emordnilap wrote:

adam2 wrote:1) They cant be turned off, so a power failure at noon, during daylight, will fully discharge the battery before darkness falls and the light is needed.

Surely a sensible addition would be a light level sensor? They’re built into every cheap and nasty solar garden light (and my car has several, phones have them too) so it can’t be difficult.

AFAIK this would not be permitted.
In public buildings, it is required that the "emergency lights illuminate upon failure of mains supply" End of !
Without the introduction of light sensors, time controls, presence detectors or other features.

Whilst such requirements would not be applicable to most domestic applications, I recommend that in the interests of simplicity and reliability, that fittings intended for public buildings be used in the home.

adam2 wrote:In public buildings, it is required that the "emergency lights illuminate upon failure of mains supply" End of !

Ah, right, the dreaded.