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Harald Schützeichel

How to measure social impact of a solar lantern?

Millions of solar lanterns are distributed in rural areas of developing countries. Most of the distributing or manufacturing companies are demonstrating the social impact of these lanterns with impressive figures. But the statements about the nature and extent of the social impact diverge greatly. This creates increasing confusion. Here are two examples for the current confusion in the impact measurement:


One solar lantern = one kerosene lamp

The count seems as obvious as accurate and easy - but only at first sight! Because they do not take into account the brightness of a lamp. And the impact differences between a mobile 25lm reading lamp and a mobile 300lm room lamp are of course significantly large.

A small lantern with only 25lm is just bright enough to enable one person to read a book. Such a lantern hardly will replace the use of a kerosene lamp in a household. It is rather the case that households with a small 25lm reading light often still use the kerosene lamp precisely because the light is not sufficient to cover all lighting requirements. Therefore, a small 25lm reading lamp does not replace the use of the kerosene lamp, but complements it for a specific, limited application.


But anyway the count "1 solar lantern = 1 kerosene lamp" is seldom used today, since it is not possible to achieve with it those great impact numbers that donors and investors want to hear. Therefore, the following counting method is now mostly used:


People illuminated

For this way of counting, there are two variants: the first indicates how many people can use a mobile solar lamp at the same time. Unfortunately, these are obviously less with a 25lm reading lamp than with a 300lm lamp. So to be fair, the differentiation should be more precise, what is laborious.

Therefore, most companies / organizations have moved to a simpler counting method, which also has the charm that the impact number will be even greater: it specifies the total number of people who could potentially use the lamp available in a household.

Instead of the number of how many people actually use at the same time a lamp (real impact), in this case the number of people who have "access to a solar lantern" in a household (potential impact) will be taken into consideration. A significantly more abundant number for marketing purposes since this way a 25lm lamp brings an impact for the same number of people as a 300lm lamp. Even if thus, of course, the real impact will be strongly adulterated.

Here is an incomplete overview of recent available impact calculations regarding the number of people who (theoretically) benefit from a solar lamp:

  • 2.8 people/lantern: Lighting Africa
  • 3.4 people/lantern: Little Sun
  • 4.5 people/lantern: SolarAid / Sunny Money
  • 5 people/lantern: Barefoot Power
  • 5 people/lantern: Greenlight Planet
  • 5 people/lantern: Waka Waka
  • 5 - 6 people/lantern: D.light

For all calculations it is indifferent that they do not take into account the brightness and thus the actual impact of a solar lamp. Therefore, the impact figures are untruly the same for a 25lm reading lamp as a 300lm lamp.



Undoubtedly, mobile solar lamps have an impact. The very arbitrary counting methods today available however are increasingly misleading. They suggest amongst others a numerical impact, which in reality is not achieved.

While nowadays there are standards in the technical area for solar lamps, it is surprising that so far no one has attempted to standardize the social impact measurement. However, the difficulties in enforcing such a quality management for impact measurement are obvious: as presumably many companies / organizations would have to significantly revise downward their impact numbers.


Harald Schützeichel is Founder/Director of Stiftung Solarenergie - Solar Energy Foundation and Founder/CEO of SunTransfer. 


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CommentsCoSend Harald Schützeichel is Founder/Director of Stiftung Solarenergie - Solar Energy Foundation and Founder/CEO of SunTransfer. 

Comment by Kat Harrison on October 3, 2014

Interesting comments and as an organisation that invests a lot in research and impact measurement of solar lights I can definitely provide some input. 

While what you say about 1 solar light doesn’t equal 1 kerosene lamp in terms of service (in many cases it’s better), our follow up research with solar light customers at SolarAid shows that on average a family does replace the regular use of 0.9 kerosene lamps as a result of purchasing that solar light, and that is predominantly with customers who bought a 25 lumen, entry-level light (note, in some countries it is higher: in Kenya the replacement ration is actually 1.76). While many ‘stack’ lighting, as you say, 40% of customers we’ve interviewed totally eliminate their spending on kerosene after solar light purchase. So, when you say ‘such a lantern hardly will replace the use of a kerosene lamp in a household’, that doesn’t seem to be the case from our experience. 

Regarding people illuminated, the 25 lumen solar lights are often used by different members of the household, so while the counting may not be the number of people using the light at the same time, the indicators used often talk more specifically about the number of people that have access to or the opportunity to use the solar light. In this way it is more talking about awareness and exposure rather than parallel usage. In any case, the SolarAid figure you have quoted states exactly that – the number of people with access to the light. It is inaccurate to say that we are indifferent to the actual impact of the light; that is exactly what all our indicators are tracking. 

You make reference to the fact that ‘no one has attempted to standardize the social impact measurement’ – there is a working group at the Global Off-Grid Lighting Association that is doing exactly that and is working alongside others trying to do the same, such as the SE4All framework. The group will be publishing and sharing its work so the calculations, assumptions and limitations are transparent. 

Harald Schützeichel is Founder/Director of Stiftung Solarenergie - Solar Energy Foundation and Founder/CEO of SunTransfer.