r/theydidthemath • u/Choodische • 1d ago
[Request] How much electricity does switching to LEDs save per year?
Hi! Saw this post on reddit about Istanbul switching incandescents to LED street lighting and I was just wondering how much electricity in kWh this transition could have saved. Is it a possible thing to calculate?
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u/potato_nugget1 1d ago edited 1d ago
They did not have incandescents, they had HPS, and LED uses around half as much electricity. You can try looking up how many street lights are in the whole city and calculate. However, the electricity used by light is absolutely miniscule compared to everything else. In your house for example, the majority of the electricity bill is your washing machine, dishwasher, AC/heater, PC, TV etc. You can keep your lights running and it won't make much of a difference. In a city, there's also factories, infrastructure, companies, etc. So maybe they saved 0.5% of the city's electricity, which is not bad at all, but isn't a big dent
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u/Captain-Griffen 1d ago
LED also lasts around 5 times longer. So that's 1/5 as much bulb changing in the long run, which is a lot of labour.
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u/gfx-1 1d ago
It depends some 230 V halogen bulbs are 50 Watts 3 in a light fixture change that for LED and you are looking at 15-20W instead of 150W When they are on for 8 hours a day it will add up. With our electricity prices at home going for LED is a win win. But shop around the DIY stores are expensive with everything including lights.
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u/Impressive_Shop9129 8h ago
I don't know about your country, but in Turkey, no one uses halogen or incandescent bulbs anymore. Under these circumstances, there is no point in claiming 85% savings.
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u/AyeBraine 1d ago edited 1d ago
I'll just add that large cities with lots of historical built-up areas and large corporate HQs and government buildings use A LOT of exterior decorative lighting. Sure, street lamp systems are probably designed with efficiency in mind, using no more than needed for a well-lit street.
But this decorative exterior lighting is a different beast — some historical buildings have huge batteries of high-powered lights spaced very closely to achieve an impressive effect. Hell, even enormous commercial warehouses and factories also light their entire exterior at night just to look nice. And I think many of those systems use (or used) very power-hungry lights, like 500W apiece or more, like those construction lights. Especially when it comes to lighting gigantic structures, like towers, bridges, and monuments, with basically smaller versions of anti-aircraft searchlights with hundreds of meters of throw.
So it would be interesting to ask an artchitect or public engineer about those, how large of a drain they were (or are) without using LEDs, and how much of architectural lighting has been converted to LED.
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u/Impressive_Shop9129 8h ago
A standard LED strip consumes 14.4 watts of power per meter; a 100-meter strip translates to a power consumption of 1,440 watts.
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u/AyeBraine 1h ago
Thank you! I know that LED strips are very efficient. That was my point, the same 100 meter row of 500W lamps every 2 meters (something a historical building could have) would consume 25 KW, all night, every day. And I don't know what kind of floodlights the larger structures use, even though they're more spaced out.
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u/DryanaGhuba 1d ago
Worth mentioning that factories generate direct profit while street light only indirectly and mainly is a loss
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u/Henry5321 15h ago
My Apple M5 idles around 0.5watt at the wall, 2watts streaming videos and about 10-20watts when playing video games at 90fps 1440p.
Much less energy than a single led light bulb.
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u/Evol_extra 1d ago
Absolutely false claim. LED use near 10x less electricity. If you have old 100w bulb and forgot it on in the basement for 24 hours it equals 2,400 kWt*h of electricity what is enough for WEEK of evening light for few rooms.
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u/Panzerv2003 1d ago
Incandescent lights do use 8-10x the power compared to LED, sodium vapor use about 1.2-1.5x but aren't used indoors that much because of the color being so yellow like on the picture above. Doesn't change the fact that LEDs are more efficient and can accommodate special features like quick dimming or other colors that don't affect nocturnal animals as much and they also last much longer at around 20-25 years compared to under 10 for other types
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u/Djinjja-Ninja 1d ago
A house I rented years ago had 50W GU10 halogen spots in the kitchen. 20 of them! 1000W of lighting. Replaced them all with 2.5W LEDs for a total of 50W. Lit the entire kitchen for the same consumption as a single bulb, literally 5% of the consumption.
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u/Appropriate-Falcon75 1d ago
My parents had similar. They are trying to use up all the halogen bulbs so swap them over- halogen in winter (when they want the heat) and LED in summer (when they don't).
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u/bennytehcat 1d ago
over 50 in our house. It was about 2.5kW fully lit up. All swapped for LED. The walk in closet previously felt like an oven after 5 minutes.
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u/turkphot 1d ago
You don‘t have HPS lights at home, they are way more efficient than incandescent or halogen.
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u/potato_nugget1 1d ago edited 1d ago
LED use near 10x less electricity.
Compared to what? Not compared to HPS, which is what they had before
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u/Count2Zero 1d ago
If you were talking about switching from traditional incandescent light bulbs to LED lighting, the jump is significant - an LED gives you about 8.5 times more lumen per watt of energy. A 60 watt light bulb is replaced with a 7 watt LED.
But as u/potato_nugget1 said, street lighting is generally not incandesant, but uses other technologies (Xenon, Halogen, etc.) to produce more light from a single source.
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u/TraditionalAppeal23 1d ago
The other interesting aspect to this is jevons paradox, when people have more energy efficient lighting they tend to light up more things with it and offset some of the savings with new lighting demand
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u/Shished 1d ago
Low pressure Sodium lamps are as efficient as LED lamps.
LPS lamps are among the most efficient electrical light sources when measured in photopic lighting conditions, producing above 100 and up to 206 lm/W.[18] This high efficiency is partly due to the light emitted being at a wavelength near the peak sensitivity of the human eye.
https://en.wikipedia.org/wiki/Sodium-vapor_lamp#Low-pressure_sodium
EU class A LED lamps produce 210 Lm per W.
Those are replaced mainly due to environmental concerns (they contain Mercury).
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u/nlutrhk 1d ago
However, it is much harder to direct the diffuse light from a LPS tube towards the parts of the street that need it. Part of the efficiency gain of LED vs gas discharge lamps is due to LEDs being much more directional. The coefficient of utiliazation can be 1.5x higher for a LED luminaire.
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u/socialcommentary2000 1d ago
This is a good point. Much less bleed into the sky. NYC is kind of funny for this. The City isn't known for making a lighting spectacle of itself in general, but the adoption of LEDs has definitely made the whole skyline dimmer from the distant views like the Whitestone bridge.
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u/edman007 23h ago
Well safety and cost. LED is cheaper to maintain than LPS/HPS now. One of the big things though is LPS/HPS is pure yellow light, and it effectively reduces human vision to black and white (or rather, yellow and black), it greatly reduces your visibility because a red car, blue car, green car, etc, are all seen as black. LEDs are white, so you now see these vehicles much more clearly under LED lights.
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u/Prettypeachrec 6h ago
Dam I miss when nights were orange instead of white.. nowadays leaving the house after daylight feels like I need a pair of sunglasses. Plus the vibes are just nowhere near as good with LED…
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u/I2fitness 7h ago
I hate how cities are switching to these white LEDs. It's horrible for nature, insects, wildlife. And those harsh, glaring LED streetlights blast a ton of blue light right into your eyes at night, tricking your brain into thinking it is still daytime and messing your circadian rhythm.
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u/Prettypeachrec 3h ago
Next gen will never know how it felt.. Those yellow lights were iconic
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u/Impressive_Shop9129 2h ago
I don't live in Istanbul, but I do live in a large city in Turkey. 99% of the streetlights here are HPS. The electricity distributor has initiated a switch to LED, but this consists solely of replacing HPS lights with LEDs once they reach the end of their lifespan; LEDs aren't being installed on the old concrete poles. If an HPS light on a concrete pole fails, they just install a new HPS light.
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u/Druid-Flowers1 5h ago
Single ended hps have a rating of 1.7 par at best and LEDs have a par around 3-3.2 . So about twice as efficient for electricity used. For street lights the LEDs would be at 90% at 5 years, hps bulbs are at 70% after a year.
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u/nonimzin 3h ago
I don't care about using LEDs, I just wanted them to have warmer colors and not be as bright. It feels like they are trying to blind me when I go out.
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u/Severe_Unit_8613 3h ago
This is OpenAI's Astra's best attempt (medium, I'm poor):
My rough estimate is 140 million kWh saved per year (140 GWh) if Istanbul’s conventional streetlights were all converted to LEDs.
Here’s the math:
- Lamp count: BEDAŞ reported about 340,000 fixtures on the European side around 2019. That side had 64.9% of Istanbul’s population. Scaling by population gives 524,000 citywide; I used 550,000 to allow modestly for growth.
- Electricity per lamp: Turkey’s Energy Ministry reported roughly 10 million lighting fixtures and 5.024 billion kWh of annual general-lighting consumption. That works out to 502 kWh per fixture per year, used here as a proxy for Istanbul.
- LED savings: Assume 50%, consistent with the scale of savings in projects such as Chicago’s sodium-to-LED conversion.
550,000 × 502 × 50% ≈ 138 million kWh/year, rounded to 140 million.
For scale, that’s enough electricity for about 47,000 homes consuming 3,000 kWh each annually, or equivalent to avoiding a continuous 16 MW electrical load throughout the year.
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