Refrigerators, cold rooms and other similar structures are provided with one or more internal lamps that are automatically switched on when the door is opened.

At present the automatic switching on of said lamps takes place by means of a mechanical switch positioned in correspondence with the edge of the refrigerator or cold room, the inner edge of the door being provided with a protrusion or tooth or other element that acts on said switch (or vice versa).

Due to the repeated switching on and off and to the particular nature of the environment where they operate, said mechanical switches often function inconstantly and imprecisely, and they end up with breaking.

The special solutions and protective measures adopted for these switches do not eliminate the problem completely.

In order to overcome the drawbacks mentioned above, a new device for the automatic switching on of the light without

mechanical contact in refrigerators and cold rooms has been designed and implemented.

The new device comprises a lamp and a circuit that senses when the door is open, constituted by several elements and operating stages.

All the components of the new device are contained in an airtight casing that can be fixed to any point of the room to be illuminated and not necessarily in correspondence with its door.

The operating principle of the new device is based on the fact that it senses the light coming in through the door that is being opened.

When the door is opened, the device senses an increase in the quantity of light that comes in and activates the switching on of the lamp.

The device periodically switches off the lamp and checks the amount of light present in the room : if the door is open there is light and therefore the device switches on the lamp again, while if the door is closed there is no light and the device does not switch on the lamp.

In this way the mechanical parts don't wear out and the user can be sure that the light will be switched on as soon as the door is opened.

Furthermore, in the case of large cold rooms, if the door is closed, but there is still someone inside, the light remains on for a given lapse of time, so that the person can reach the exit.

The circuit that senses the presence of light and manages the operation of the lamp comprises several elements and stages, and precisely a sensing stage, a triggering stage, a switch-off timer, a power management stage, a power supply stage and a negative feedback stage.

The sensing unit comprises a phototransistor in darlington configuration with a BC 237, which ensures considerable sensitivity. When light enters the room (door opening) the potential on the Q1 sender increases.

This causes the switching over of the IC1 comparator (LM 311) that enables the triggering phase.

The other inlet of the comparator (operating threshold) is connected to other 2 transistors in darlington configuration.

In this way considerable sensitivity and thermal stability are obtained, since the two thresholds move in the same direction (though maintaining the same relative distance) as the temperature varies.

This feature is fundamental for a device that operates in a very wide temperature range (-40+50).

The sensing unit is provided with a light sensor, usually a phototransistor (for example in darlington configuration with a BC 237). Even the minimum light makes the potential increase, while the phototransistor is earthed when there is no light at all.

Even the minimum light enables the triggering stage.

The triggering unit comprises a NE555 in astable configuration, which triggers the control timer for the switching on of the light.

This ensures that the timer is triggered whenever there is light inside the room.

The switch-off timer comprises a NE555 in monostable configuration and determines how long the light remains on. This lapse of time can be set approximately between 30 seconds and 10 minutes.

The power management unit comprises an optotriac insulating element that ensures the maximum safety. The optotriac directly pilots the triac that feeds the lamp. In this way perfect insulation between the sensing circuit and the lamp power supply circuit is guaranteed.

The power supply unit comprises a circuit that regulates and stabilizes the power supply to the whole sensing circuit.

The negative feedback unit is a circuit that delays the successive switching on of the light in order to avoid undesirable oscillations.

It is possible to provide the circuit that senses when the door is open with an acoustic signaller and an additional timer to be set and connected to the timer that controls the switching on of the light.

When the light is switched on, the additional timer starts counting and is set to zero as soon as the door is closed again.

When the door is open and the additional timer reaches the time set, the acoustic signaller is operated, in such a way as to warn the user that the door is still open.

Furthermore, the device described above can be provided with two electrical contacts (NC contact-NO contact) that for example can be used to switch off the refrigerator fan when the door is opened. The two electrical contacts are piloted by the light control.

The following is just an example among many of the invention in question, illustrated in the enclosed drawings, wherein : -Figure 1 shows a possible electronic diagram of the sensing unit (SI), in which the phototransistor (Q5) that senses the presence of light can be observed.

-Figure 2 shows a possible electronic diagram of the triggering unit (S2), the switch-off timer (S3) and the negative feedback unit (S4).

The three units (S2, S3, S4) are connected to one another in order to obtain the optimal operation of the circuit.

-Figure 3 shows a possible electronic diagram of the power management unit (S5) and the power supply unit (S6).

Upon implementation the device and/or its elements can be realized with different dimensions and shapes that are all included in the inventive concepts expressed in the following