Here are some helpful tips to follow:
1) Use fresh spinach for photosynthesis studies. Check to make sure it is fresh and that leaves are turgid because wilted spinach will yield poor results, as will spinach that has been treated with preservative sprays.
2) We recommend an LED grow light, such as the Taotronics E27 12w LED Light. This light provides the correct wavelengths for photosynthesis with very minimal heat. This type of light can be found from suppliers like Amazon.
3) We recommend using a heat sink (especially if you are using a halogen or incandescent bulb) so that the temperature in the area of the sensor stays relatively steady. A tissue culture flask (~100 cm2) or a large beaker (~1000 mL) filled with water works well. Keep the lamp 6-8 inches from the heat sink. If the lamp is too close, it will cause the heat sink to warm more quickly than desired.
Note: We used to recommend a 35 W halogen, flood-beam bulb or a standard 60 W incandescent bulb, however both of these bulbs have become difficult to find. Both types of bulbs (especially halogen bulbs) also radiate a lot of heat energy so using a heat sink (see Tip 3 for additional information) is very important for most types of bulbs.