Because many discharge and cheap LED lamps emit unevenly across the spectrum, with a spike in green that no single white balance setting fully removes. The published figure that bears on it is a colour rendering index, and most lamps do not state one.
A cast is a statement about the light, not about the camera. What makes fluorescent and low-quality LED light hard is that the statement is uneven.
Why green in particular
These sources emit in peaks rather than smoothly. The peaks commonly fall in the green part of the spectrum, so the camera — which measures an average — records a scene where green is over-represented and everything else under-represented relative to daylight.
What the two published figures do
Colour temperature, in kelvins, locates the overall colour. Eight titles here publish one. It is what white balance corrects.
A rendering index describes fidelity under that light, and four titles publish one. It is the figure that predicts whether reds and skin will look right, and its absence on a listing is itself information.
The practical order
Photograph a neutral reference under the light and set white balance from it. Then, if colours still look wrong, the lamp is the problem rather than the setting — replacing or adding a source with a published index is the only real fix.
Why mixing makes it worse
Two sources at different temperatures put two casts in one frame, and no single white balance corrects both. A bi-colour panel published with a range — one here states 3200 K to 5600 K — exists to be matched to its neighbours rather than to be set at random.
What people ask before they commit
Will a custom white balance fix it?
It corrects the overall cast and cannot fill in what the lamp never emitted. Setting white balance from a neutral reference under that light is the right first move and it leaves some colours — reds and skin especially — looking wrong in a way no single adjustment reaches.
Which figure should I look for on a light?
A rendering index, published by four listings in this catalogue and absent from the rest. Two panels can both state 5600 K and render a red jumper differently, because the temperature locates the colour of the emission while the index describes how faithfully colours appear under it.
Last reviewed 12 September 2026