Sun heat radiation sensor

DETAILED DESCRIPTION An aim of the present invention is to provide a relatively cheap device capable of measuring the heat or infrared radiation received from the sun.
Typically, but not necessarily exclusively, this information is used to provide an indication of the sun-tanning power of the sun.
According to one aspect of the present invention there is provided a device for providing a visual indication of the amount of heat radiation received from the sun at any time, the device comprising carrier means and a plurality of display areas on the carrier means each comprising a different, heat dose activatable liquid crystal composition arranged to receive heat radiation from the sun, characterised in that the liquid crystal compositions are selected to be activated in response to different relatively narrow temperature ranges within a wide temperature range that the liquid crystal compositions would be expected to be heated to when the device is exposed to heat radiation from the sun, whereby a quantitative visual indication of the amount of heat radiation being received from the sun at any time is provided by the change in appearance of the display areas in dependence on the temperature that each liquid crystal composition is heated to by the sun within said wide temperature range.
The device may include at least one filter for filtering the sun radiation.
For example, the device may include a U.
V.
filter to prevent or reduce degration of the liquid crystal composition by U.
V.
radiation.
The device may also include a filter to obscure some, but not all, heat frequency bands of the heat radiation from the sun.
However the use of such an I.
R.
or heat radiation filter is not preferred.
The reason for this is that, in use of the device on a sunny day, the thermochromic liquid crystal compositions will be heated both by the ambient air temperature and by the heat radiation from the sun.
When the heat radiation from the sun is not blocked or filtered it will normally be capable of heating the liquid crystal compositions to far higher temperatures than the ambient air