Night orientation light
A night orientation light (short night light ) is a lamp that spreads a weak but constant light and thus enables spatial orientation in relative darkness.
Tasks and areas of application
Night lights are mainly used in bedrooms to aid orientation without additional lighting when waking up and getting out of bed at night, for example when going to the toilet . This is possible because the pupils are very dilated at night and therefore the eyes are very sensitive, so that even very weak light is sufficient to recognize objects and obstacles in the room. Photopic vision , i.e. vision with color perception , is not given in weak light, but is usually not necessary for orientation. Switching on the room lighting should be avoided, as a light of normal strength with nocturnal dilated pupils is perceived as unpleasantly dazzling as long as no adaptation has taken place. There is also no need to fumble for the light switch in the dark, which reduces the risk of accidents (especially for elderly or frail people).
Night lights can also help the most in children spread fear to diminish before dark. The fear of the dark is known as achluophobia (also: nyctophobia). For this purpose there are night lights with child-friendly motifs and shapes.
A special function of night lights is that of emergency lighting of escape and rescue routes . In this function, however, night lights can only be used temporarily in the private sector, because according to building regulations, special formal and technical requirements apply to emergency lighting that conventional night lights do not meet. In particular, emergency lighting must be independent of the normal power supply in order to ensure that it functions even in the event of a power failure .
Energy supply and consumption
Since a night light burns permanently or at least for long periods of time, low energy consumption is a main criterion for the design of the lamp and in particular for the selection of the light source (see below).
The power consumption of conventional night lights with energy-saving lamps is between 0.2 and 2 watts. With 1 watt of power and an electricity price of around 28 cents / kWh, electricity costs of around € 2.45 / year with uninterrupted operation (even during the day) result.
If the duty cycle is reduced, energy consumption and costs decrease accordingly. For this purpose, night lights are partially equipped with a light sensor that automatically switches the light on when it is dark ( twilight switch ). Pay attention to the power consumption of the sensor circuit.
There are also night lights with motion detectors in stores ; however, this does not normally make sense, since the continuous internal power consumption of a common motion sensor is similarly high or even higher than that of an energy-saving night light.
Thanks to the low power consumption, the night lights can also be supplied with energy from batteries or rechargeable batteries instead of the socket . In this way, night lights can also be used for mobile use or as emergency lighting (see above). Luminous periods of a few hours are achieved in continuous operation (calculation example: a light with 0.3 W power causes a current of 200 mA when powered by a battery with 1.5 volts; with a nominal charge of the battery of 2000 mAh , the lighting period is about 10 h).
Light color
It is beneficial to use red light for night and orientation light. When it is dark, the eye forms a pigment ( rhodopsin ) that increases the eye's sensitivity to light. The rhodopsin is broken down by white light in an extremely short time, the light sensitivity of the eye is greatly reduced (one is almost blind). Red light has no influence on the breakdown of rhodopsin. The high sensitivity of the eye is retained, the eyesight is good - even if the color is falsified, which is not a disadvantage for simple visual tasks. The mentioned conditions are the reason why z. B. light displays at night inside a motor vehicle are often red or orange.
Bulbs
Various light sources are used as the light source in night lights . The main criterion is the energy consumption.
- Glow lamps (color mostly reddish-orange or green, sometimes recognizable by flickering, not suitable for battery operation due to excessive voltage)
- Electroluminescent lamps,
- LEDs (increasingly common)
- Low-power incandescent lamps (rare, as they are actually unsuitable for continuous use due to poor light output and high power consumption)
- Fluorescent lamps (rare, not available for low power)
- Tritium gas light source (very rare, does not need a power supply).