The sunshield acts as large parasol allowing the main mirror, optics, and instruments to passively cool to 40 kelvins (−233 °C; −388 °F) or cooler,[6] and is one of the enabling technologies that will allow the JWST to operate.[11] The kite-shaped sunshield is about 21 by 14 metres (69 by 46 ft) in size,[12] big enough to shade the main mirror and secondary mirror, leaving only one instrument, the MIRI (Mid-Infrared Instrument), in need of extra cooling.[6] The sunshield acts as a V-groove radiator and causes a temperature drop of 318 K (318 °C, 604 °F)[13] from front to back.[12] In operation the shield will receive about 200 kilowatts of solar radiation, but only pass 23 milliwatts to the other side.[14][12]