**The torch powered by BODY HEAT: $35 Lumen generates a small electrical current when held in the hand **
By VICTORIA WOOLLASTON FOR MAILONLINE
Forget batteries and wind-up generators, a designer has created a torch powered simply by human touch.Called Lumen, the small device is fitted with a panel that converts body heat into an electrical current to power a small LED.The tiny torch is only 1.6-inch (40mm) long and weighs just 35g, meaning it isn't the most powerful of light sources, but it said to produce a similar brightness to flashlights fitted to smartphones.Lumen was designed by New York-based Ross Zhuravskiy.It features a ceramic bar that acts as a thermoelectric generator (TEG) to harvest energy from a user's body heat when they touch this bar.Thermoelectric generators convert differences in temperature directly into electrical energy.Lumen takes into account the ambient air temperature and can therefore determine when it is being touched.
The metal body of the Lumen is then said to act as a 'radiator' to retain this heat.Mr Zhuravskiy has set up a Kickstarter campaign to fund production of the device and, at the time of writing, has raised more than $39,150 (£25,285) with 25 days to go.His target was $5,000 (£3,230).'In my application, the difference between the temperature of your body and the environment is enough to generate power for single LED,' he explained.'We can't power high-output LEDs with a small TEG', however Lumen can produce around 15 mA at 3 volts when there is a relatively small difference between the body heat and environment.The example given on the Kickstarter campaign is the difference between 27°C (82°F) air temperature and a finger with a temperature of 36°C (98°F).'When the difference is bigger, excess power is stored in a capacitor to power Lumen whenever you need it,' Mr Zhuravskiy added, and this energy is enough to power a 5mm LED with 3000 mCd light output.
MCd stands for millicandela and is used to measure light output. The light produced by a 3000mCd is said to be comparable to the flashlights in phone.To put this into perspective, indicator LEDs fitted to gadgets and panels, for example, are typically in the 50mcd range, while 'ultra-bright' LEDs reach up to 15,000mcd.Lumen torches are available from Kickstarter in aluminium and titanium and prices start at $35 (£22).For an extra $15 (£10), the Lumen can be fitted with a tritium vial.These vials are glass tubes that have light-producing tritium gas inside.Lumens fitted with these vials produce a small amount of light to help users find the torch in the dark.