The structure of plants is regulated, in part, by light signals from the environment (Hoenecke et al., 1992; Franklin et al., 2005; Kim et al., 2007). Light is the energy source for photosynthetic organisms, and light intensity plays an important role in plant growth. Low light conditions inhibit plant growth and productivity by affecting gas exchange (Zavala and Ravetta, 2001), whereas excess light intensity has detrimental effects on the photosynthetic apparatus (Lichtenthaler et al., 2007). As a result, plants have developed sophisticated mechanisms to adapt their structure and physiology to the prevailing light environment. In our study, the low PPDF of 50, 150, and 200 mol m−2 s−1 induced lower health index for young tomato plants, indicating that low PPFD were not suitable for their growth (Table 2). Along with the increase of the light intensity, SLA always gradually decreased, and the decrease in SLA may reduce the light energy absorption.