VIIRS nighttime lights vs. DHS survey data for rural electrification monitoring
A portfolio team tracking a rural electrification loan usually has two numbers in front of it: the DHS electrification rate from the last survey round, and whatever the implementing agency reports on connections made. Neither updates monthly. Nighttime lights data gets pitched as a third option, a satellite proxy that fills the gap. It's worth being precise about what it substitutes for, because it isn't a substitute for the survey itself.
What DHS surveys measure
Demographic and Health Surveys ask a household, directly, whether the dwelling has an electricity connection. That's a binary, self-reported answer, collected at the household level, aggregated up through a sampling frame to produce a rate for a region or country. It captures connection status for the people living there, including households that are connected but barely use power, and households with a line running past the door that never got hooked up.
The constraint is cadence. DHS cycles run roughly every three to five years in a given country, and the questionnaire changes over rounds, so even trend comparisons need care. For a project with a five-year disbursement schedule, that can mean one survey at appraisal and one near closeout, with nothing in between except whatever the implementing agency self-reports.
What VIIRS nighttime lights measure
VIIRS is a satellite sensor recording light radiance at night, at roughly 500 m resolution for the standard product (coarser derived products run at 250 m or wider depending on how they're processed). It doesn't ask anyone anything. It records whether light is present over a pixel, and how bright, on a monthly basis.
That's a proxy for grid presence and use, not a direct read of connection rates. A settlement can show rising light and still have a DHS electrification rate well below what the glow suggests, because light picks up streetlights, commercial premises, diesel generators, and solar lanterns along with grid connections. Conversely, a newly connected but sparsely populated settlement can register barely any change in a 250 m or coarser pixel because the light simply isn't dense enough yet to register against the sensor's noise floor.
Where the two disagree
The gap between a DHS household-electrification figure and a satellite light-intensity reading usually comes down to three things: what counts as "electrified" (a meter versus a bulb that turns on sometimes), what the pixel can physically resolve (a cluster of ten rooftops near the detection limit versus a market town), and timing (a round of DHS fieldwork captures a moment, light data accumulates month over month).
None of that makes nighttime lights wrong for what they're used for. It makes them the wrong tool for estimating a household electrification rate directly, and a reasonable tool for answering a narrower question: is light spreading across the settlements in this program area between now and the last data point, or isn't it.
Where nighttime lights actually help a portfolio team
The gap DHS leaves open is exactly the period between formal survey rounds, which is also the period when a results framework needs a progress signal and the loan committee is still asking for one. A monthly light-intensity read over the settlements named in the project documents won't tell a team the household electrification rate. It will tell them whether the settlements that were supposed to get grid extension this quarter show any change at all, months before the next survey round could confirm it either way.
Electrification Map builds exactly that kind of read: a monthly panchromatic nighttime-light pass over the settlements in a financed program area, so a portfolio team has something to look at between DHS rounds instead of waiting on the next survey cycle to find out whether anything moved.
If a project's results framework has gone quiet since the last survey, it might be worth seeing what a monthly light read over those same settlements would show.