LED displays
The value of LED: reliability and energy
An LED screen looks expensive to buy. But over its lifetime that picture tilts: high reliability and low energy consumption make it more cost-effective in the long run than the alternatives.
An LED screen costs more money at the start than an ordinary sign. But it lasts a very long time and uses little electricity.
One LED screen can also show many different messages, so it actually replaces a whole stack of fixed signs. Over the years it is therefore often cheaper, and you can change the content at any moment.
The value of an LED screen only becomes clear when you look at quality and cost over the entire lifetime, not just the purchase price. In terms of legibility, LED outperforms traditional technologies: in a study by the US Federal Highway Administration (1998), LED signs were legible over greater distances than flip-disk and incandescent signs, for both younger and older drivers.
Long lifespan
LEDs last a very long time. Under ‘worst case’ assumptions (continuously on for 100,000 hours, or well over 11 years, with day/night temperature swings), one can assume with 98.33% certainty that the LEDs will not need to be replaced. That high reliability is a large part of the value.
Low energy consumption
LEDs consume far less than incandescent lamps. According to the same source, one pixel (a group of four LEDs) uses about 40% less power than a comparable incandescent lamp. Long lifespan plus low consumption amply offset the higher purchase price. Modern LEDs have since become even more efficient and brighter.
The reliability R was calculated with R(%) = e^−(λ₁t₁ + λ₂t₂) × 100, with the assumptions: directly driven (not strobed), on 100% of the time (100,000 h), half during the day (t₁ = 50,000 h, 45 °C, λ₁ = 0.0003/1000 h) and half at night (t₂ = 50,000 h, 5 °C, λ₂ = 0.000037/1000 h). That yields R ≈ 98.33%.
Legibility comparison (1991)
| Technology (character height) | Day, young | Day, old | Night, young | Night, old |
|---|---|---|---|---|
| Fibre optic (16 in) | 1006 | 959 | 687 | 667 |
| LED (17.8 in) | 812 | 681 | 794 | 602 |
| Flip-disk (18 in) | 731 | 667 | 363 | 348 |
| Incandescent (18 in) | 800 | 671 | 750 | 569 |
| Hybrid LED/flip-disk (18 in) | 731 | 667 | 794 | 602 |
Legibility distances in feet. In all cases LED was more legible than the incandescent lamp; at night, with young observers, LED even overtook fibre optic.
Total cost of ownership
The TCO reasoning: higher CAPEX, but low OPEX thanks to energy savings (pixel ≈ 0.5 W versus ≈ 1.25 W for an incandescent lamp in a comparable sign) and virtually non-existent replacement costs over > 10 years. One reprogrammable screen also replaces several static signs. Since 2004, LED efficiency (lm/W) and lifespan have increased further, making the TCO balance even more favourable.