How to build a light bulb drier – food dehydrator

Food dehydration and preservation are necessary to improved food security, nutrition and income generation leading to empowerment in the developing world.

Using a variety of development resources including appropriate technology to utilize available resources in solar thermal energy, smoking food, and electricity – this project – to produce heat and accelerate drying.

Understanding the principle behind food dehydration facilitates this development process. In any simple food dehydrator the principle remains static. A fuel source is used to generate heat, which creates a thermodynamic system. This artificially created air transfer works to remove moisture from food and act to preserve it – slowing the decay and defilement of the food by microorganisms.

A low-placed air inlet allows for the entry of cool air into the system, a heat source raises the temperature of the gas, exciting it and causing it to rise, as it passes over the food, moisture is drawn into the warm air, that air then escapes at a controlled rate for a raised chimney/vent.

With that understanding a variety of drying devices can be constructed – solar tent driers, cabinet driers, box driers, sulphur driers, smokers (slightly different) etc.

In my community, we’re in a sub tropical climate. Meaning greatest food availability is during the highest humidity and rainfall seasons. This creates issues with implementing solar driers.

Noting this issue, I discovered that my community has some resources we might be able to use. Solar panels linked to deep cycle 12v batteries (what’s in your car) and put through an inverter. But there are precious few in my community that have this resource – including my clinic and basic school.

In response to these limited resources, I took the principle and adapted it to my area. Using only locally available materials I constructed a light bulb drier. I afterwards priced these materials in my nearest town (56km) – those prices are reflected in the list.

Material list:
1 100w bulb – clear 2000kwa
1 light fixture (from my clinic)
1 2M length of electrical cord 2.5mm or larger (clinic)
1 plug end – these three bought together 18000kwa
1 roll of aluminum foil (5m)- local shop 14300kwa
1 piece of wire mesh 3000kwa
1 3m piece of bamboo – split 1000kwa
1 cardboard box – clinic drug kit delivery box – free
1m of tying wire (made by un-weaving one row of wire mesh) – free

Starting with the box, I cut s tight-fitting hole for the light fixture, then three 2x2cm square ventilation holes on the bottom left of the box. And 1-2x2cm chimney hole in the top right flaps. This orientation facilitated the passage of air across the box.

I then lined the inside of the box with aluminum foil, as well as the box flaps. This acts as an insulator and reflective surface – it is preferable but not necessary if you use mud brick, wood or another material to make your box.

Then using the wire, I lashed the bamboo into a tray. I had cut it into four short legs, and two long and two short pieces to fit inside the box. This is your drying shelf/tray

I then added my shelf to the box, inserted a light bulb into the socket and adjusted and tray height to prevent burning/issues with the proximity of the light bulb.

I plugged in the system to test placement and heat generation. The system ran a little hot so I added a second air chimney. This cooled the system.

I then added two sliced and peeled apples, two peeled and wedge-separated oranges, and a cut up fresh lemon. I closed the box, plugged in the system and checked back every 2 hours. The apples took 8 hours to completely dry, the oranges 10 and the unpeeled cut lemon 12. I then ate my handiwork – it was fantastic.

For a total of 26860kwa or on a rate of 5100kwa to 1 USD – $ 5.26

Some other considerations. Other materials can be used for your drying box, as well as other bulbs at lower wattages. Mudbrick – a natural insulator, wood, plastic (Jerry cans) metal, clay, even cement can be used. Although these will change drying times etc.

Remember all that needs to be preserved is the airflow dynamic and heat.

Oh, also, bananas, mangos, mushrooms etc can be dried using some basic techniques – peel, cut etc to allow proper dehydration. Lemon juice also helps to maintain hygiene.


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