Thus the artists staring moving towards the idea of 'outdoor studios.' Plein air painting became popular with the Impressionist circle in the 1860's.It refers to the outdoor painting done under natural daylight conditions, from direct observation of a subject or motif. There were basically four plein air effects - side light, back-light, front-light, top-light, and gris-clair. Side light is the most sculpting and produces shadows that give the effect of a relief. Side light is able to generate the most equal balance between masses of lights to darks, or warms to cool hues. Back lighting highlights the contrast of dark tones to light tones. Front- lighting, the most brilliant is used to minimize shadows and undermines the illusion of depth. Top lighting also referred to as zenith lighting was a sign of order and was used for the human form. Lighting from below implied disorder and was notorious for producing monstrosities. Gris-clair is the term for bright indirect daylight without shadows and local color is at its most genuine form in this light and tonal contrast is minimum. An indispensable tool associated with plein air painting was the painting parasol. Artists were afraid that because of the brilliant sunshine, they would make their studies too black and upon returning to the studios, will no longer be able to see a single detail in the picture. The parasol was useful too in reducing reflected light from the wet paint surfaces itself that often tired the artist's eyes and also provided protection from rain. Other tools necessary for outdoor painting were portable paint boxes, common place items by this time, had been sold fully fitted and equipped from early in the century. Pocket sized boxes held on the thumb and variants supported by a shoulder strap were also used to assist the artists in the outdoors.