Replacing HPS with LED: flux, power and payback

The high-pressure sodium (HPS) lamp is the most common lamp in the warehouses, production halls, streets and fuel stations of Uzbekistan. It gives a lot of light per watt, so the promise of “three times less electricity” from replacing it with an LED luminaire does not hold. Below is an honest calculation: what a one-for-one replacement gives, where the larger gain comes from and how not to lose illuminance.

What is installed now: the HPS numbers

Three numbers the replacement is calculated from. All three are rated values from manufacturers’ catalogues, and all three sit in our savings calculator.

• Power. An HPS 250 W (SON-T) lamp does not run without a ballast, and the meter sees the lamp together with it. We take 275 W: 250 × 1.10 under the EU energy labelling convention for discharge lamps on external control gear. That is a lower estimate: at the minimum ballast efficiency of 85% the system can draw up to 294 W. HPS 150 W: 165 W; HPS 400 W: 440 W.
• Flux. A new HPS 250 W lamp gives 30,000 lm (Lisma DNaT 250-5M); the premium Philips SON-T PIA Plus gives up to 32,800 lm. HPS 150 W: 15,750 lm; HPS 400 W: 52,000 lm.
• Depreciation. By 16,000 hours the lamp must retain at least 85% of its flux (the minimum requirement of EU Regulation (EC) No 245/2009, table 13). Rated life in the Lisma catalogue is 24,000 hours, so at 12 hours a day the lamps are replaced every 5 to 6 years, and for the last year or two they give 15% less light.

Lamp flux and luminaire flux are different quantities: the reflector and the glass of an old housing absorb part of the light. We do not know that efficiency and do not include it, so in the comparison the old scheme looks better than it does on site.

One-for-one replacement: an honest 25% to 45%

Take our suspended Prom: flux from the 2018 IES files, not from module promises. Prom 200W: 26,000 lm at 200 W; Prom 150W: 19,500 lm at 150 W.

• HPS 250 W to Prom 200W: 275 W against 200 W, 27% less power. Flux 30,000 against 26,000 lm, 13% less. The calculator shows a warning here, and rightly so: a luminaire-for-luminaire replacement does not pass on rated flux.
• HPS 250 W to Prom 150W: 45% less power, but also 35% less flux. Not to be done without a recalculation.
• HPS 150 W to Prom 150W: 165 W against 150 W, almost no saving (9% less), but 24% more flux.
• HPS 400 W: we have no model with an IES file at 52,000 lm. Two Prom 200W give exactly 52,000 lm at 400 W against 440 W, 9% less.

On 120 HPS 250 W luminaires at 12 hours a day and 300 days a year, a one-for-one replacement with Prom 200W removes 32,400 kWh a year: 118,800 against 86,400. At a tariff of 1,100 UZS per kWh including VAT (Cabinet of Ministers Resolution No. 243 of 15 May 2026) that is 35.6 million UZS a year and 9 kW of freed capacity. Payback at the price from the model card is about 57 months. That is the truth about a “lamp for luminaire” replacement against HPS: it pays back, but not within a year.

Where the gain is larger: three sources

There are sites where the power halved after the replacement and illuminance went up, but the gain there came from the calculation, not from the lamp. Three reasons.

First, recalculation to the norm. Old schemes were calculated from the lamp that was in stock, not from the norm. A typical plant driveway on 27 HPS 250 W gives ≈ 30 lx at rated flux where the Uzbek building code ShNK 2.01.05-24 (table 15) requires 4 to 6 lx for category V service roads. 27 bracket-mounted Classic 100W meet the norm at ≈ 2.7 kW instead of ≈ 7.4 kW. This is worked through in the solution for streets and grounds.

Second, directed light. With a lamp in a round reflector a noticeable share of the flux goes to the roof and the upper rack tiers. The light distribution curve of an LED luminaire (it is recorded in the IES file) puts the light on the floor and on the rack, where it is read. That is why in a warehouse 60 HPS 250 W (≈ 16.5 kW) are replaced by 75 Prom 100W and Line 100W luminaires at ≈ 7.5 kW, and illuminance in the aisles goes up.

Third, depreciation. The LED luminaire in this estimate degrades too, but it has no 15% drop in flux by the end of the lamp’s life and no lamp replacement every 5 to 6 years with a lift.

How to check before you buy

• Ask for a DIALux calculation from the site plan, with the target under ShNK 2.01.05-24 and the maintenance factor from app. 1, table 3 (0.67 to 0.71 for clean production halls, 0.63 to 0.67 for streets). Layout and count come from it, not from a “one-for-one” ratio.
• Check the flux in the calculation against the luminaire’s IES file, not against an “up to N lm” figure from advertising. Our files sit on the IES page: they date from 2018, and we say so openly.
• After installation, measure illuminance with a lux meter over a grid of points: at acceptance ShNK 2.01.05-24 (clause 178, table 26) allows no less than 90% of the design level.

The case figures on this page are estimates marked ≈, not guaranteed until measured and recorded. The calculated saving holds under the stated assumptions: hours, days, tariff, maintenance factor.

Frequently asked questions

Can an HPS 250 W lamp be replaced with a 100 W LED luminaire?

Not on flux: 13,000 lm for Prom 100W against 30,000 lm for the lamp, 57% less. Such a replacement saves electricity at the expense of light. If a calculation to the norm shows the old scheme is over-lit several times over (as happens on driveways and in warehouses), a 100 W luminaire is suitable, but the calculation decides, not the power.

Why does the calculator show a flux warning?

Because the rated flux of a new HPS 250 W lamp (30,000 lm) is higher than the flux of Prom 200W by IES (26,000 lm). The lamp rating ignores the losses in the old housing and depreciation, so the real drop is smaller than calculated, but the calculator has to say so. Take the count from DIALux, not from the ratio.

How many LED luminaires are needed instead of HPS 400 W?

We have no 52,000 lm model with an IES file. The option that keeps the flux is two Prom 200W per lamp: the same 52,000 lm at 400 W against 440 W. More often a recalculation to the norm shows that so much light is not needed.

What do we warrant on a replacement?

A 3-year warranty on the luminaire, production in Tashkent since 2014, flux from the IES files. The savings percentages and payback are calculated under the stated assumptions; the LM-79 test report on the assembled luminaire is still in progress.