# Will a servo stabiliser that holds an oil mill's lights at 210 volts save electricity, as the Alwar manual says?

Canonical: https://senseible.earth/answers/alwar-oil-mill-lighting-210-volt-stabiliser-report

The Bureau of Energy Efficiency (BEE) Alwar manual cuts lighting from 240 volts (V) to 210 V with a servo stabiliser and books 12% of a 15 kilowatt (kW) lighting load, but its sum uses 1.5 kW, which is 10%. Over 3,500 hours that is rupees (Rs) 25,200 a year. Test your own lamps first.

## What the manual sets out

- Lighting at 240 V now, 210 V with a servo stabiliser. Saving written as 12% of the light load, with a lighting load of say 15 kW, 3,500 hours a year and Rs 4.8 a kilowatt hour (kWh).
- The manual's background: in discharge lighting, a 10% fall in supply voltage gives a proportional 10% drop in power and an insignificant 1 to 2% drop in illumination. It says most of the plant's lighting is discharge type, rated 205 to 210 V.
- Printed sum: 1.5 kW x 3,500 hours x Rs 4.8 = Rs 25,200, or Rs 0.25 lakh a year.
- Cost for the units in Alwar and Sawai Madhopur: Rs 0.21 lakh. Saving printed as Rs 0.21 lakh. Payback 12 months.

## Three things that do not line up

- 12% of 15 kW is 1.8 kW. The sum uses 1.5 kW, which is 10% and matches the manual's own 10% rule; the 12% matches the 12.5% fall in voltage. At 1.8 kW the saving is Rs 30,240.
- The sum gives Rs 0.25 lakh for one 15 kW lighting load, yet the cluster saving is printed as Rs 0.21 lakh, which is less. Our reading: the cluster row looks like one circuit, not the cluster.
- A payback of 12 months is Rs 0.21 lakh over Rs 0.21 lakh. Against the Rs 0.25 lakh of the sum it would be 10 months.

## Does lowering the voltage save power? It depends on the lamp

Our note, not the manual's. 240 V to 210 V is a 12.5% fall in voltage. A plain bulb is a resistor, so its power falls with the square of the voltage, here to about 77%, which disagrees with the manual's proportional claim for plain bulbs. A tube on a choke falls by less. A light-emitting diode (LED) lamp's driver is built to hold its power steady, so it saves little or nothing. Light output falls too; the manual puts the fall at 1 to 2% for discharge lighting. The live page on voltage optimisers says the same: only some loads respond.

## How to test it

1. List the lamp types and watts on the circuit.
2. Read a lighting sub-meter, if you have one, for two weeks with the stabiliser bypassed and two weeks in service, at the same working hours.
3. Count only the kWh you measured, and walk the floor to check the light is still enough.

## The manual's sum and the 12% sum

- Manual: 1.5 kW x 3,500 hours = 5,250 kWh x Rs 4.8 = Rs 25,200
- At 12% of 15 kW: 1.8 kW x 3,500 = 6,300 kWh x Rs 4.8 = Rs 30,240
- Carbon dioxide (CO2) at 0.675 kg a kWh, the financial year 2025-26 grid factor: 5,250 x 0.675 = 3,544 kg, about 3.5 tonnes. 6,300 x 0.675 = 4,253 kg
- Cluster row: Rs 0.21 lakh / Rs 4.8 = 4,375 kWh x 0.675 = 2,953 kg, about 3.0 tonnes
- Voltage: (210 / 240) squared = 0.77, the fall for a pure resistor only

Load, hours and tariff are the manual's, at its date. Only a measured saving counts.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so your monthly kWh from the bill is on file to compare with the months after the stabiliser. A separate lighting sub-meter reading is custom, on request. It does not control voltage or know what lamps are on a circuit.

- [Do voltage optimisers and servo stabilisers save power](https://senseible.earth/answers/voltage-optimiser-servo-stabiliser-savings)
- [Rice mill voltage stabiliser report](https://senseible.earth/answers/rice-mill-voltage-stabiliser-kwh-saving)
- [Do the Alwar manual totals add up](https://senseible.earth/answers/alwar-oil-mill-manual-totals-checked)
- [Carbon calculators](https://senseible.earth/calculators)

Sources: [Bureau of Energy Efficiency and Confederation of Indian Industry, Manual on energy conservation measures in the Alwar oil mill cluster (SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/Alwar_Oil%20Mill.pdf), [Central Electricity Authority, CO2 Baseline Database for the Indian Power Sector (grid factor 0.675 kg CO2 per kWh, financial year 2025-26)](https://cea.nic.in/cdm-co2-baseline-view?mappingId=234&lang=en)

Last reviewed 2026-11-06. Figures are the manual's, from the Bureau of Energy Efficiency Small and Medium Enterprises (SME) programme. Its saving is an estimate, not a measurement. Measure with the stabiliser in and out before you rely on it.