This apparatus is designed for determining Planck's constant based on the knee voltage of a range of LEDs, and associated frequency of the light emitted by the diodes. This version does not use a photocell. The diodes are a UV, an IR and three which emit visible light. They have been carefully chosen to have a very narrow and well-defined bandwidth. The equipment is simple to use and doesn't require special light sources or costly filters. The results are reproducible to within 10% of the table value for Planck's constant.
Power is supplied by a built-in 9 V battery (included), or a 9 V mains adapter may also be used.