L70 vs L90 Lifespan: What the Numbers Mean

What L70 and L90 mean

L70 and L90 are lumen maintenance figures. Lumen maintenance describes how much of an LED's initial light output remains after a stated period of use. On a grow light listing, L70 means the light still produces 70 percent of its original output when it reaches the hour figure the maker states; L90 means 90 percent of the original output remains at its stated point.

The numbers matter because every LED slowly loses brightness as it operates. The L value names the point a maker has chosen to describe that decline. An L90 figure is a stricter milestone than an L70 figure because the light reaches 90 percent of original output earlier than it reaches 70 percent.

Both figures appear in hours on a maker's specification sheet, alongside other performance details. The listing title usually does not carry them. Read the maker's product page and the manual that ships with the light for the exact hour figures, and start with the buying guide for an overview of what to compare across models.

How L70 and L90 compare

L70 is the conventional benchmark in the lighting industry. Many general-purpose LED products use L70 as their stated useful life. L90 is a more demanding milestone that appears on products positioned for longer service.

When two lights list the same hour figure for L70 and L90, the one with the L90 figure is being held to a stricter standard at that point in time. When one light lists L90 at a higher hour figure than another, the maker states that the first retains 90 percent of its output for longer, assuming the makers used the same measurement method.

Comparing L70 and L90 between two models works best when the maker states both figures in the same unit and method. When a seller does not publish either figure, the listing is incomplete for that detail, and the maker's page should be checked.

This site compares grow lights on their stated details, and the L70 and L90 figures are part of those details when a maker publishes them. The figures are the maker's estimate, not a guarantee of how any single light will behave. For an overview of how the comparison works, see the best LED grow lights guide.

Where the figures appear on a listing

Grow light listings usually show the light type, wattage, coverage area, dimmer and timer in the title and bullet list. L70 and L90 values appear less often in the title and more often in the specification section or on the maker's product page, such as the Vivosun page for a model.

The DesignLights Consortium page for horticultural lighting explains that products in this category make performance claims that are verified according to published standards. L70 and L90 figures are examples of performance claims a maker publishes, and the qualified products list is one place to see products whose claims are documented.

The manual that ships with the light also lists the L70 and L90 figures when the maker publishes them. Keep the manual with the warranty documents so the figures are easy to find later. The warranty and lifespan article explains how these documents relate to a light's stated service life.

What the numbers tell you about long-term value

L70 and L90 figures tell you how long a maker expects the light to stay near its original brightness. A light that reaches L90 at a later hour figure than another light is described by its maker as retaining 90 percent of its output for longer.

For a grower who plans to run lights for many seasons, a later L90 figure is a detail worth comparing between two shortlisted models. For a grower replacing a light after a short project, the difference matters less. When you compare models, be sure to compare the same milestone: compare L90 to L90, not L70 to L90.

The figures do not predict plant growth, light intensity for a specific plant, or efficiency. They describe only how the light's brightness declines over time. The maker's manual and page are where to read the full specification, including the hour figures. For guidance matched to your space, see the bar light guide and the quantum board guide.

What they do not tell you

L70 and L90 say nothing about the light's spectrum, coverage area, or dimming range. A light with a strong L90 figure may still be the wrong type for a small shelf of houseplants if it is a large panel.

The figures also do not describe the light's intensity at a given distance or how plants respond to it. For those details, read the maker's published specification and the plant's light requirements. The University of Minnesota Extension page on lighting for indoor plants explains that different plants need different light levels and that insufficient light causes problems like leggy growth.

For a small shelf of houseplants, a clip-on light or a strip pack may fit the space better than a large panel, regardless of its L figures.

Questions to ask the maker

When the listing does not show L70 or L90 figures, the maker's product page or manual usually does. Ask the maker for the hour figures if they are not published: "What L70 and L90 hour figures does the specification sheet state?"

Also ask whether the figures were measured according to a published standard, and whether the light uses a driver or other components that affect how long the light keeps its stated output. The answers are part of the stated details you can compare between models.

If you prefer a light with Samsung diodes, check the L figures on the maker's page before choosing, and compare models in the Samsung LED grow lights guide.

What to pick for your job

Questions

What does L70 mean on a grow light listing?

L70 is a lumen maintenance milestone. It means the light still produces 70 percent of its initial light output at the point in time the maker states in hours. The hour figure appears on the maker's specification sheet and manual.

What does L90 mean?

L90 is the same kind of milestone with a stricter threshold: the light retains 90 percent of its initial output at the stated point. Because 90 percent is closer to the original output, a light reaches L90 earlier in its life than L70.

Which number matters more for a grow light?

Neither number is better on its own. Compare the hour figures between models for the same milestone. A later L90 hour figure means the maker states the light keeps 90 percent of its output for longer. Read the figures on the maker's page.

Are L70 and L90 figures guarantees?

No. They are the maker's stated estimates based on their published method. The DesignLights Consortium page notes that performance claims in horticultural lighting are verified according to published standards; the maker's manual and product page are where to read the method and the figures for the model.

Do L70 and L90 predict plant growth?

No. They describe how light output declines over time, not how plants respond. Light needs vary by plant, and the University of Minnesota Extension page explains that different plants require different light levels.

Where do I find L70 and L90 figures?

The listing title rarely carries them. Look in the specification section of the listing, the maker's product page, and the manual that ships with the light. When the figures are not published, ask the maker.